Ugh, I'm really opposed, as an OSX and iOS user, to Apple having this direct of a tie to any social networking company. It would be awful if they avoided adding more sharing options and OS integration for 3rd-party applications like Facebook because they could be a competitor to Twitter or any other investment. I'd rather they stay as relatively neutral as they can.
I'm not sure. I think to myself I'd rather have the development time spent elsewhere in the operating system, but whether it'd make an actual difference in reality is a guessing game.