As for humble bundles, just claim the key and then give it away. Once its activated, that account gets the game forever.
So if you give me a key and I activated it, then its my game. Not sure how it works for bundle websites because you will still have the key there, but you can't activate it since I already did.
Unfortunately Native Linux gaming is going really slow and Windows gamers are not convinced that their games will run yet.
Hence our website and dedication to proving those games CAN run in Linux.
I prefer native too, but I already own waaaaay too many games that are Windows only. I still want to play those.