The usual "Don't dig for gold, sell shovels" type thing and in this case the analogy holds up very well.
The SC2 players are digging for gold and only a few of them make a big strike and the casters and distributors are the ones making all the cash selling shovels.
One could argue that, while being a successful professional gamer is hard and rare, it's probably much harder and rarer to be a successful caster of professional games. Casters also have to tackle a broader range of skills: they have to remain very current with the game they cast (and they're generally expected to be above-mediocre players themselves), they have to understand the production and distribution process (audio, screen capturing, uploading to Youtube/other video site, etc.), and most of all, they have to get and maintain fans.
Many of the casters are skilled players themselves. Artosis (one of the commentators for GSL) was quite highly ranked. I believe Tasteless and his brother Day9 are as well. What's interesting to me is Husky, who I don't think is anywhere near their skill has the largest audience.
I've got friends who don't play starcraft who watch husky and love it like it's any other sport. So I definitely agree there is a lot of skills involved and even different target markets. The hardcore players like the best player/casters. There appears to be an even larger casual/not playing at all audience that enjoys the sheer entertainment value of esports.
Pretty impressive. Much of this money likely goes to further tournaments and such anyways so a lot of the money is probably finding its way back to players.
The SC2 players are digging for gold and only a few of them make a big strike and the casters and distributors are the ones making all the cash selling shovels.