I've got to agree, however I think a large reason for this is the fact that almost every indie game gets accepted. I think if an indie studio wants to make a name for itself then they need to release their game on a tighter platform where they will face less competition. Ideally if they could get their game on WiiWare they would have a lot less competition and a larger market to target.
I think right now the indy market on Xbox is similiar to Flash gaming. Their are way to many games for any of them to be extremely successful. In order to make it you need to have a product that is far superior to anything else on the market.
If you get your game on WiiWare it would also not be hidden rather up front with all the other games. Easy to find and alot of people would buy it on impulse. PSN is the second worst with many more games to compete against. Microsoft's X-Box is the third worst and I'd say then comes Android and finally iOS. Fact is the market is getting flooded with Indie games and if the developers want to make anything of themselves they will choose to play on a level playing field.
If they go to WiiWare or PSN or even Steam they will have a much better chance at competing with competitor's then they do on X-Box or iOS or even Android!