No, there is only one .com Registry: Verisign. There's multiple Registrars (the companies you as an individual typically buy your domains at) for .org just as there are for .com
As far as I know, you can't "pay off" a domain. And most of us are at some usually negligible risk of losing a domain by mistake or because someone bigger wanted it.
Not having a central authority does not require a bizarre technological solution. You just... Have multiple authorities. You don't even need software to do that. But if you did use software to make management easier, you still wouldn't need blockchain.
For each TLD, there is only one registry. This is true for .com as it is for .org.
In many (most?) cases, there are multiple registrars, which is who the end customers use to “purchase” their domain from. The registrars (plural) register the domain with the registry (singular).