Earlier quoted context omitted.
I think different schools have different philosophies as far as that goes. There are schools that admit to the department and have students do very little research for their first two years, and there are schools that admit by advisor and you start research immediately. My PhD was the latter, but for me it was actually one of the major selling points for me on the program. I had a pretty good idea of the area that I…
With regard to your first paragraph, I don't think there are any American universities that admit students by advisor. As far as I'm aware, your admission is a decision made solely by the graduate admissions committee. Even if you have an advisor ready to take you on the most they can do is recommend you to the committee, not supplant it. When you're admitted there are still criteria aside from research to work on. I…
Nothing you say is wrong; you're correct that everyone has to do course requirements. But culturally the course requirements are treated as a distraction from research, and students are expected to start working primarily on research from their first semester. I think this is more or less the case in all top American CS PhD programs, and there are reasons to set things up this way, but it's a very different environment from PhDs in most other fields.