I think everyone can agree that Linux's biggest shortcomings on desktops/laptops are the graphical and audio part. So, even though I agree with "As soon as someone is willing and able to put in the effort on desktop Linux, it will be as good as it is in those other areas." I would replace "someone" with "every vendor".
I feel like most vendors (NVIDIA/ATI/Wacom/whatnot) concentrate much more of their effort into supporting Windows and even OSX becasuse thay's their audience.
Also, I remember reading somewhere that NVIDIA/ATI work closely together with Microsoft because od Direct X[citation needed, though]. I had the opportunity to work with Direct X (the new API) and I found it much more pleasant than working with OpenGL (even though I ended up using OGL in the end; I used Windows and DX to simplify prototyping, because doing the same thing in OGL required much more dev time, at first atleast).
EDIT: Also, let's not forget how most of the majority of linux developer community neglects GUI and the overall end-user friendliness, and how the environment is in most cases quite hostile towards UX/GUI designers in general. There are, of course, exceptions, but those are few.
While it is a vendors issue, they don't just randomly support hardware. They go where the big guys are. As you say NVIDIA\ATI contribute to Direct X, but it happens because MS makes it happen. Google dragged the cell vendors into supporting Android. Desktop Linux just needs a backer that is big enough to make them put forth the effort.
I feel like most vendors (NVIDIA/ATI/Wacom/whatnot) concentrate much more of their effort into supporting Windows and even OSX becasuse thay's their audience.
Also, I remember reading somewhere that NVIDIA/ATI work closely together with Microsoft because od Direct X[citation needed, though]. I had the opportunity to work with Direct X (the new API) and I found it much more pleasant than working with OpenGL (even though I ended up using OGL in the end; I used Windows and DX to simplify prototyping, because doing the same thing in OGL required much more dev time, at first atleast).
EDIT: Also, let's not forget how most of the majority of linux developer community neglects GUI and the overall end-user friendliness, and how the environment is in most cases quite hostile towards UX/GUI designers in general. There are, of course, exceptions, but those are few.