So with Windows Internet Computer Names I don't have to worry about DNS or Registrars or anything and It can be whatever I want such as p.WhateverIWant.pnrp.net and my dynamic IP doesn't matter anymore either. If it changes is this name still good? What's the catch, what am I missing?

This has some tremendous advantages over DNS. For instance, when you register a PNRP name in the cloud it is locatable across the world within a few seconds! If your IP address changes your PNRP registration is also updated, so you don’t have to worry about people connecting to stale addresses.