The problem is that getting people to try a game that has received almost no marketing or other exposure to the public, is extremely difficult.
I doubt I'd have bought Sanctum for $30, or Magicka or Trine or Revenge of the Titans.
I didn't even know about those games until very shortly before their release dates.
The lower price point of Indie games allows them to be a more tempting buy for many people.
The great thing about this(that Cliffski seems to be missing) is that any indie developer is free to set any price they want on a game. I'd welcome an experiment from him where he sets the price that he thinks his games should be sold for and see what happens.