There's a really good article in Toronto's Eye Weekly which explains how writers really run teevee shows, and who does what. What it doesn't explain is how the networks seem to be doing everything they can to screw up teevee (though they seem to indicate that somehow David E. Kelley might someday be brought to justice for his crimes against teevee).
The big difference between film directors and TV writers comes down to the work itself. Film directing is a solo job; co-directors are as rare as Siamese twins. Television writing, however, is a collaboration. The exceptions are David E. Kelley, who wrote most of the episodes of Ally McBeal and The Practice by himself, especially the crappy ones, and J. Michael Straczynski, who wrote 92 of the 110 episodes of Babylon 5.
There's also an additional Village Voice article about how indie film directors are finding they can do their best work in teevee.
TV's new artistic credibility is making the small screen an alluring alternative for directors, offering freedom from the stresses of financing and distribution that beset any adventurous filmmaker. "Up until a couple of years ago, if you went to direct TV, you didn't tell anyone because there was such a stigma attached to it," says indie film producer Christine Vachon. "But now some of the HBO and Showtime series show more provocative things than we can get into movie theaters." According to film and TV director Barry Levinson, "Movies these days are less and less about characters and behavior. All that's gone out the window. It's television that's taken over the role of capturing the small moments of human behavior—a role that's been abdicated by theatrical films."