That's a relatively new take on things, though. It is a fact that attitudes toward television have changed in Hollywood since premium cable channels started producing their own shows. The difference didn't initially happen in the medium, which was always able to develop characters over a longer period of time; it happened in the $$$. Paid cable channels devoted much more money to developing programming and also took away the need for advertising interruptions, both of which made television much more attractive to writers. That produced more quality television, which in turn continued to attract more writers and then better actors and directors. Also cinematographers, which is much overlooked, I think -- the fact that television now often looks as good as movies, when it used to be limited to a sound stage and one or two outdoor locations, makes an enormous difference in the way audiences perceive television, even subconsciously.
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.