Since 140 characters aren't enough to fully explain the reasoning behind my recent tweet, here it is:
The idea of being independent is to not depend on publishers, and in the pc indie-games market Steam and Humble Bundle are slowly starting to wield the same powers that publishers do in the AAA world.
Basically, they are seen by many developers as a "get out of jail free" card - just get on Steam or HIB and you'll be swimming in the river of money in no time! Their powers are getting to the point where I think many developers consider "getting on steam" and "getting in a bundle" as a crucial part of their financial strategy.
That situation is just not good for keeping indie games independent. You just switch one devil for another. Instead of making games that you think you can get a publisher behind, you make games that you think will get on Steam or a bundle.
I must say that I believe they have not yet wielded their powers for evil. Nevertheless, I don't like the fact that they have these powers at all and could (ab)use them any moment if they wanted to. Who knows if they won't at some point get under financial (or other) pressure that might change their morals?
Personally, I don't want to bet on the good guys remaining good indefinitely when presented with great power.