There is no irony, I think there is just confusion. The Windows license is much more restricting, you are never going to be able to ship Windows for your customers alongside your Windows kernel module unless you/they pay for Windows. GPL allows you to distribute Linux for your customers at your behest as long as you satisfy certain requirements, namely, source. The way I view it, it is not adding restrictions whatsoever, it is actually adding allowances. More permissive licenses add even more allowances.