SC2 may have the biggest pro scene, but Halo/Black Ops have far bigger player bases and are mainstream titles that dominate the gaming market. Regardless of how small their pro scenes are, sponsors are reaching a very large, lucrative demographic by supporting them. And of course as team games, they're going to have bigger prize pools. As the SC2 scene grows and bigger sponsors arrive, the prize pools will get bigger.
Right now Europe has a very impressive crop of talent and a community that is constantly working together/practicing to get better; they also have a bunch of online tournaments and some big live events. Meanwhile the NA scene is basically dominated by the exact same people who dominated during the beta two years ago. We've got some of the most tournaments but the player base is weak, and lazy. Once Korea turns its full attention to SC2, I fear NA will be left in the dust. We'll see companies continue to partner with Koreans, get sponsors, then send them around the US winning shit.
I definitely think more needs to be done to cultivate a healthy pro scene in NA. I think MLG is great, but they could be doing a better job helping put the spotlight on some of these up and comers - not just from NA to be fair, but also from EU. They really need to fix the points system/rankings or it will just continue to be dominated by the same crop of lackluster players being rewarded for being on big name teams. InControl is honest enough to admit he hasn't played well and doesn't deserve his ranking, and that applies to many other people. Let's get some fresh blood in there and build careers. Cruncher is pretty much the last NA guy I can remember who managed to make a name for himself.