I think they're saying that most things that go over TCP are HTTP, which means usually those bits are set to 80 or 443. With SRV records we could be using more

I think they're saying that most things that go over TCP are HTTP, which means usually those bits are set to 80 or 443. With SRV records we could be using more ports, and then presumably do port based routing instead of host based routing on the back end.