>Maybe they don't want to get into the targeted advertising market and see themselves more as general advertising?
Then I think they completely missed the boat.
The whole conceit of twitter is _you decide_ who to follow. They don't even start you out with a Myspace-esque Tom. Every user's timeline is unique.
So, if I'm following Roger Ebert, Kevin Smith, and Netflix, don't you think I would be receptive to DVD advertisements? Similarly, if I'm following Pogue, Mossberg, and Gruber, wouldn't I be receptive to iPhone app ads?