How does Ethereum domain registration works?
So the whole point of a name reg contract is not to send transactions, rather its sole purpose is to build up a database which other nodes can then query.

Ethereum smart contracts have immutable storage. This means that you can prove your primacy to a specific name, and other people can then reference that as part of a database. 

What it comes down to is the credence other entities hold towards a specific name reg Dapp (Network effect, utility, what service it is registering names for etc). In some situations people would want a name reg for a specific purpose, say a list of Escrow contracts for one company, this could then be used internally, or shared. In others as you mention in your question, people would rather look towards a singular name reg which controls a DNS service.

You can have a look at an example name registration smart contract here: https://github.com/ethereum/dapp-bin/blob/master/namereg/namereg.html

Hope you find this useful!