Wow, with all the other bundles popping up, the Humble Indie group just seems to be cranking them out really fast.
Maybe its because the developers really are enjoying this and the help with its sales.
I know that the maker of The Oil Blue (sold in the Indie Royale bundle) has stated:
"15,000 sales of the Indie Royale bundle! That's x35 what I sold on my own with the Oil Blue in 1.5 years." Link
They might make less per sale, but make a ton more sales and get better known. And with the Humble Indie Bundle being the more well known, it might be worth it to offer your games there.
*automatically refuses to place horse heads in anyone's bed*