Of course, things have changed since I graduated. No, not at all. These days research has become a really big business, and large American universities especially have hopped on the bandwagon because they can augment their income via research. They hire faculty that already have a proven research record and ability to capture large amounts of funding. The scientist with the reputation basically does very little other than write proposals and travel around the world doing public relations.
Someone has to do the research, and that's where the post-docs come in.
So a lot of research gets done, a student gets a degree and then goes on to a post-doc themselves some place. This is the way that successful labs are organized. If you're an undergraduate at the University of Illinois, you are really lucky to ever see a prof. in a class. Almost certainly a graduate student, at the most a post-doc, teaches the class because the professor does not have time for teaching. I think people are starting to make noises in the States about the fact that this is not what was intended.