I've always viewed (and I'm talking about IPv4 here) that the IP layer allows two computers to exchange data, while UDP and TCP allow two processes to exchange

I've always viewed (and I'm talking about IPv4 here) that the IP layer allows two computers to exchange data, while UDP and TCP allow two processes to exchange data. In other words, IP names a computer, and UDP/TCP name a process. It's probably not really needed for IPv6, but the concept was carried over since it was already there.