Bill I am not sure I agree totally with you..
You are correct that GS incorporated variation sounds and not just the GM standard of 128 patches.
But from day one the Sequence programmers go to standard has been GS [actually a true GS as in Roland GS instruments]..even today it is the standard..

Although the new PC's have the licensed standard GS wavetable..it does not behave as a Roland GS product..
They use the standard GS potential differences from GM , but do not utilize the variation sounds[tones] and drum kits accurately as a Roland Hardware piece, or Roland's GS software..

I don't believe Yamaha's XG has the same broad appeal[except Yammie people]...