Comment by johnnyanmac

Humble bundle uses steam keys, so they are working in tandem regardless.

That said: enforcement on such things is not going to be 100%. Larger companies will either be purposefully ignores or make their own internal deals and contracts to follow. Some smaller games will slip through like everything else in life (Valve can still let Malware slip in once in a blue moon. I'm not surprised you can find some niche Japanese game sold for cheaper on DLsite or wherever).

But the point is that they can push thst in devs because of the monopoly. And that's how you get stuff like the Wolfire lawsuit when a few people do push back.