And I agree that most "common" users could use Bing and not know the difference, but then again that destroys the U.S's whole case of a "monopoly" market.
This is more of a discussion of walled gardens than typical monopoly abuse.
Some video game streamers on youtube reach 50k+ viewers regularly and donations of $10+ just keeps raining in with that audience. That isn't any less than top Twitch streamers, and the Youtube will only grow since it is so much easier for people to discover Youtube streaming than Twitch streaming.
So really I don't see Twitch being a major player in a few years. There is no reason for content creators to stay with Twitch once youtube gives them a bigger audience and more money.
If you're interested in some tips on a game and search for it (maybe "In game X I'm having trouble on this level") chances are you'll get some hits from youtube of people running the level as a walk-through - twitch highlights don't tend to be as indexed or as accessible since the metadata about what's actually in the video is a lot weaker by default.
Those hits on folks looking for a walk-through will end up with some conversions to stream subscribers and I think that's why Twitch is really destined to struggle.
Youtube is attempting to move into Twitch’s space with live-streaming, but Twitch is certainly not competing with youtube as a video hosting product. Vimeo is the primary competitor there, and I have no idea how good a job they’re doing really.
And, again with respect to video hosting there are plenty of very valid competitors technologically - with respect to search if you secretly rebranded google to bing I doubt anyone except the most techie would notice a difference - they win in search because everyone "googles it" - they used to win because alta vista, ask jeeves, lycos and yahoo were all trash, but now there is legitimate competition.