They're probably here because of the "layering" concept. If you view it from that angle, they're necessary to identify the application. Of course, they are not

They're probably here because of the "layering" concept. If you view it from that angle, they're necessary to identify the application. Of course, they are not really used that way nowadays... except by firewalls maybe, so even more stuff is moving to 80/443. They are kind of useful sometimes if you consider port < 1000 privileged, although that's also quite limited.