For people who are interested in the business story behind the Humble Indie Bundles, the creators gave a talk covering Bundles 1 and 2 at the 2011 Indie Games Summit:
As a Windows user - seeing that the software available for different architectures says to me that the code is more than likely robust and well debugged.
The thing is you have no guarantee that the Windows binary have been generated after the port was done. Also, no guarantee it's the same source tree and not different forks of the same base.
http://www.gdcvault.com/play/1014437/The-Humble-Indie
One of the take-away messages they had was "always target Mac and Linux, because it's a bit more work but you'll double your revenue".