And yet, for about a year with Time Warner, YouTube was the ONLY bad site. Constant and endless buffering. Until I set my preferred video to 720p. And then it ran much faster than the 240p, 360p or 1080p.

Then someone told me this could be fixed by switching to Google's DNS and sure enough it went away immediately.

Speed. In the old days, telephone lines were EXTREMELY slow and they wanted to limit that to just the actual transaction details. Also, they would only call a modem when that transaction actually happened.

But you're right, for modern operations, they should just be dumb terminals.