I suspect the GS softsynth provided by MS was written for them by Roland.

The Yamaha XG softsynth was pretty good but when you can still pick up XG hardware wavetable PC soundcards for not a lot of money whats the point (except for portable users, of course!)? If your souncard is described as using the YMF 724, 734 or 744 chipset you've got a 32 voice XG hardware wavetable synth.

I think I've seen this chipset on some IBM and Sony notebooks as well.