My hazardous guess would be that their average percentages are the same, but the era is where it would differ. Linux compatibility for newer titles is where Linux is lacking, but the support for older titles is pretty fully fledged.

Likewise, Microsofts compatibility with older titles is pretty abysmal but is probably comparable to compatibility with newer titles on Linux.

That said, over time I have a feeling MS will continue to go down and Linux will continue to go up.