And it's cyclical: the quality is so high now that I think it *has* started to change the medium. Better actors, directors and writers raise the expectation of, e.g., strong character and thematic development over time. The advent of DVD and the internet means that things will be analyzed, referred back to, put in full context: that absolutely affects how these things are put together.
Now it's so widespread that it's moved even to non-premium cable channels. Television used to be very much the second tier for actors and directors and writers, the thing that you did when you couldn't get work in movies. Now it's evened out so much that the pendulum is almost starting to swing to the other side. We talk about this ALL the time in my field. It's very quickly moving toward the point where television is depleting most other fields of its best writers -- as well it should, with how well it's advanced.