OK, let's get specific:

PTR requires delegation from the authoritative server for the IP address, and this is wholly separate from the registrar process. Many folks don't understand how PTR works vs. how standard A records work. If you don't understand it, you don't know you need to talk to your hosting provider about this delegation.

Many folks also don't understand how the PTR is used in validating sending mail servers. And many folks have a hard time grasping that you only configure one PTR for each IP address (see? I'm talking fundamental misunderstandings of DNS here, and no DNS server or GUI can fix them, though gods know we've tried). Finally, you'd be surprised how many people intentionally configure a PTR that does not resolve in the other direction, thus breaking mail.

Most folks are dealing with many domains on a single IP address. This further confuses folks with regard to the PTR. Which name for the IP? Many folks are baffled. A basic understanding of DNS would resolve this (no pun intended). As I mentioned above, with an understanding of the way it works, most DNS problems are completely transparent.

Default TTL doesn't solve a user not understanding that when they change IP addresses, it can take as much as days for the rest of the world to know about those changes (first world will know within hours; third world caches much longer and occasionally ignores TTL). Again, I'm talking about users fundamentally not understanding how DNS works and that it is a heavily cached protocol. If you don't understand those things, having a default TTL doesn't help you when it's time to migrate to a new data center. Webmin also provides default ttl values.

Serial numbers. I have never once mentioned serial numbers in this discussion. I can't remember the last time I've heard someone who had a problem with serial numbers...actually, now that I'm thinking of it, I do remember. A user (I think a recovering djbdns user, actually) who thought they knew more than they really did wanted to argue about RFCs and whether an incrementing number or a datestamp was valid (I don't remember which, but the form he was arguing was invalid was also provably valid, based on examples found within the RFC). But, this is the kind of silly stuff that I'm not talking about. Syntax is irrelevant to my suggestion that people read DNS and BIND. Oh, and Webmin handles serial numbers in BIND, in just about any format that is valid according to the RFC.

Some others issues that I see people make:

Incorrect NS, MX, etc. records. djbdns doesn't babysit the records to make sure they point to working servers. Users occasionally try to use IPs directly in these records. BIND will error on this, as expected, but it still confuses people who don't grasp basic concepts.

Performance. People who don't understand DNS often think they can get out of it by relying on someone else for their DNS service. Like the overworked DNS servers provided free with their registrar or hosting account. On top of this, these are also the same people that make all the dumb mistakes mentioned above, compounding their confusion into a perfect storm of "nothing was working, so I reinstalled my operating system and now nothing works!" stupidity.

Fundamental misunderstandings of the protocol and the way DNS does what it does are what I'm talking about. Some DNS servers are easier to configure than others...I'll concede that. Doesn't matter. When you set out on a journey, you kinda have to have a vague notion of where you're going, or you probably aren't going to get there, even if you have a GPS.

Also, shouldn't you just go ahead and support djbdns?

Why? All the security issues that plagued BIND 4, and to some degree BIND 8, have mostly been long resolved, and BIND 9 is, by far, the world's most popular DNS server. djbdns these days is obscure, at best. You and I remember the time when it was relevant...but I'm involved enough in this aspect of the industry to know that the ship has long since sailed for djbdns; new users are not adopting djbdns on any scale worth talking about, though plenty of cantankerous old-timers keep hanging on. We get maybe one person every six months to ask about djbdns. There are so many things ahead of djbdns in our queue that it will likely never make it to the head.

nginx is our next major endeavor (which gets requested every couple of days, and has real advantages over Apache for some of our real paying customers). nginx is actually a much bigger job than djbdns would be, since DNS is already fully abstracted out of Virtualmin because of the PowerDNS module, while web service with Apache is pretty deeply ingrained. But I can pretty clearly see an upside for us in supporting it that I do not see with djbdns.

Also, the historic license stupidity of djb software has guaranteed that all of it would fall into obscurity. I guess most of it is public domain now, but I just don't see much new interest in their use.

Do you really get more requests for PowerDNS than djbdns?

Yes, we did, but we also got money for PowerDNS support. It wouldn't have happened without it being fully sponsored by a hosting provider that wanted to use PowerDNS. We don't do contract work any more, but we could help you find a developer to add djbdns support, if you'd like to see it in Webmin and Virtualmin. Or, if you know Perl, we'd be happy to assist you with getting up to speed on the module API.

Actually, it looks like there is already a third party Webmin module, of some sort, for djbdns. Though it looks like it hasn't been updated in years, and doesn't have a lot of discussion on the web about it.

Just so you don't think we hate djb, we do fully support qmail, though I happen to prefer Postfix by a large margin (and I doubt we would spend significant time on qmail today...the userbase is a fraction of what it used to be, and we rarely get questions about it).

Anyway, I'm still not really interested in talking about the relative merits of DNS servers. I don't care. They all work acceptably well, at this point, and I rarely see a BIND configuration file (I don't have a problem with BIND configuration files, but why bother? I've got tools for that).

I just wanted people to understand the most fundamental building block of the Internet a little better, and I pointed to the best book on the subject. Complaining about DNS and BIND because it uses BIND configuration files for the examples is like complaining about TAoCP because it uses MIX rather than Python (or whatever) for the examples. There is no better book on the subject of DNS, or if there is, I have never seen it.