The praise for AMD comes from releasing the documentation (what the community kept shouting about for ages). They did. They also help develop open source drivers, quite a lot, in addition to constant improvement of the binary drivers. This is far more than what people were requesting, and yet people are still unhappy about it.
However, of course driver development from nvidia and AMD has the focus on windows - why wouldn't they? That's where the bulk of the money is.
Can't say what nvidia does (it's likely something similar), but AMD actually provide more resources per market share percentage to Linux than to Windows. It's just that that Windows market share is much larger.