I agree with the sentiment, but this doesn't play out in practice because of the dancing pigs problem, which I'm sure you know, but in short basically is "[when] given a choice between dancing pigs and security, users will pick dancing pigs every time."

Malware is deceptive, ever evolving, and constantly violates user expectations in a way that you really can't stay on top of unless you devote a fair amount of attention to understanding how these things work. Mac users aren't necessarily more or less gullible than their Windows or even Linux counterparts[1], but they are used to a more relaxed experience online. When Mac malware and adware really started to hit more than it had in the past (Safari toolbars, MacKeeper, and search hijackers, etc), a lot of the users I supported just kept getting re-infected because what was once safe for them to do suddenly was riddled with malware sites that just read the UserAgent of the browser and deliver the proper payload; people who were used to searching simple stuff like "[textbook].pdf" or "game of thrones.torrent" and would just hit back when a .exe would download now had to actually watch out because they were getting .pkgs and .dmgs to install.

I think Apple's goal with the Mac App store is sound - they saw the changing environment and it was just going to be a matter of time before their users started wondering why the Mac system wasn't as protected as iOS. It's tough to sell people on the security of one of your products when the other one is riddled with adware.

Developers and power users I think all exist in the know enough to be dangerous zone, and they should rightfully know how to get applications that are deemed unsafe for the Mac App store. They certainly have to know how to turn off Gatekeeper or make exceptions to install other apps, they have to in order to get some of the common terminal tools they want, so I'm not sure how the Mac App store is the great impediment to such users.

I understand the complaints of the devs that are in the distributing in the Mac App store - 30% off the top is harsh (though the trade off I guess is that now you get access to the pool of Mac Appstore gift cards that Apple throws out every year), and you get, more or less, the Apple seal of approval. For some, like for commenter ThomPete elsewhere in this thread, the app just didn't mesh with the Appstore because of how it functioned. But for a lot of apps it's just fine - everything they need to do works well within the confines of the store, or the Devs work to create parity between the versions. Daisy Disk, one of my favorite apps I've found from the App Store, does this - there are some limitations in the App Store version, but they adjusted their license to allow parity between the two releases and ensure that regardless of where you bought it, you got the app as it was intended. I really don't think this is much of an issue at all for users who are seeking extended functionality on OS X - if you want to leave the sandbox, it's very easy to do so; just pick a direction and go. But usually the reason for leaving the sandbox is pretty intentional; a lot of the kids are pretty happy just playing in the sand with everyone else, and that's to Apple's credit, not to their shame.

The App Store more or less does what it should and does it well. Pricing needs to be adjusted, as I'd rather devs not have to sacrifice 30% off of already meager prices to the Apple beast. But it's a nice system, and I wish they'd extend it to have a proper package management system baked in, a la apt-get or pacman or yum.

[1] If you think a linux user is automatically more savvy, try sending one just about any semi-malicious bash command and tell them to try it, and watch how many will happily punch it in, even if it requires sudo, or how many will happily copy and paste any command from online without checking it first.