Yes, it always depends... NVIDIA's huge blob is probably a case where they re-invented lots of wheels in order to share the same driver between different OSes.

Yes, it always depends... NVIDIA's huge blob is probably a case where they re-invented lots of wheels in order to share the same driver between different OSes. For something as complicated as a modern GPU driver, this could well make sense from an engineering point of view (legal objections notwithstanding). On the other hand, 10 years ago there were various out-of-tree Linux WLAN drivers, and each of them contained a full independently developed 802.11 stack, perhaps one shared across drivers for multiple OSes by the same vendor - surely having this much duplication of generic infrastructure that dwarfs the actual model-specific part of the drivers is quite pointless. IMHO only GPUs have an inherent complexity that is high enough that one could think about alternatives to just using the shared infrastructure that's already in Linux. But even in this area you see companies like AMD moving towards a Linux-specific kernel driver approach with their new "amdgpu" driver.