I don't know why that stackexchange accepted answer with 41 votes was the one the questioner judged as the best. To me, it does not actually answer his question: "What do domain name registrars do for its customers to justify this extra $9.82?"

It's best to break apart that question into 2 components:

1) "What do domain name registrars do?"

2) "What justifies this extra $9.82?" <-- accepted answer explains this via the history of politics and government bumbling

To answer the sub-question, "what do domain name registrars do?" for a technical audience like webmasters.stackexchange, it would make more sense to explain the technical landscape because it's somewhat of a mystery blackbox to many people. Also by understanding this, phrases such as "monopoly over .com address" make no sense. It's not really a business monopoly but a natural technical boundary of database administration. Unfortunately, the technical underpinnings look like a business monopoly on the surface.

Imagine an absurd (but simple) scenario. You create a new TLD called .hackergeeks. You'd have to "administer" that tld. That means you literally hold the master database of records for that tld. To do that, you might grab one of your old laptops with a 100GB harddrive from the closet and load up MySQL on it to hold the registration records. You filed paperwork with ICANN and they recognize you as the master authority for .hackergeeks. ICANN does not hold the database records for .hackergeeks, you do. In turn, this means your computers are the ultimate authority for DNS resolution. ICANN also doesn't care whether you use MySQL, PostgreSQL, Oracle, or SQLite for registration records. You just need to have some type of acceptable hardware infrastructure to administer the domains. If you're just selling a few thousand .hackergeek domains, your modest laptop would work. Obviously, this is oversimplifying things but the idea is to picture some entity (that's not ICANN) literally spending money on hardware+software+electricity to maintain a database.

Now, Verisign holds over 117 million .com domains[1]. Obviously, they have a lot more hardware infrastructure to handle that capacity. Registrar resellers like godaddy or namecheap sell ".com" addresses but their datacenter computers don't actually hold the master database records for the ".com" they sell -- it's the Verisign computers that hold it. Verisign also has a larger staff to handle non hardware stuff like legal processes (2 parties dispute ownership of a domain, fraud, etc).

Once the underlying technical picture is clear as to what authoritative registrars (not reseller registrars) actually do, then the pricing question can be analyzed. We speculate that the overhead to run and maintain the master .com registration database to be somewhere between 9 cents and $7.85[2]. That's a different question involving profit margin targets, competition, politics, etc that the accepted stackexchange answer explains.

To address the "monopoly", how would a de-monopolized ".com" actually work from a technical standpoint? Again, somebody has to maintain the master database. Would we de-monopolize by having one Company ABC Inc to hold database records for A-M.com and another Company XYZ to hold records for N-Z.com? We would then have DNS servers with an if/then/else statement to route queries to the correct database? Or what if we do a SHA1 hash and distribute (shard) the ".com" database records over 10 different companies? Company A has 17 million records. Company B has 17 million records, and so on for a total of 117 million records we have today. We'd then have DNS servers burning up cpu cycles calculating billions of hashes repeatedly to send queries to one of 10 databases. Therefore saying "Verisign has a monopoly over .com" actually obscures the picture. It is more important to avoid monopoly at the entire DNS level (via TLDs) instead of the ".com" level and that's what we already have today.

With all that said, Verisign profit margins to administer the ".com" database is too high considering the falling prices of compute power and disk storage. Maybe a better scenario would be a government non-profit entity. The USA government already manages 300 million social security numbers, the millions of Federal Tax IDs for businesses, and passport IDs. Therefore, the government managing databases of unique IDs is not outside the realm of possibility. Another option might be decentralized ownership of ".com" via a distributed block chain similar to bitcoin[3]. I'm not familiar enough with it to know if it can handle the high registration activities of 117 million addresses.

[1]http://www.verisigninc.com/en_US/channel-resources/domain-re...

[2]http://www.internetcommerce.org/dotcom_price_freeze/

[3]http://namecoin.bitcoin-contact.org/