Let's say I'm a TV executive for your average cable channel, like... Animal Planet. What's to stop a channel like Animal Planet from working directly with Apple to provide content, bypassing cable companies?
Contracts.
Sister Stations like Discovery, History, etc.
the thought that Cable Companies have a MUCH larger consumer base to sell to than AppleTV owners
the thought that selling to a cable company gets them XXXXXXX dollars
selling to Apple might get them XXXX dollars due to some people not watching a show they spent a bunch of $$ making
The "big risk" factor that jumping to a new delivery format means