No comparison in the sound quality. Forte wins.
I bought it, it is very convenient as a GM synth.

I understand you want an 'official word' from PGMusic, but that may be a question better asked of the Coyote team, as to how the license works.
If the sounds are already licensed in Windows, making use of them thru DXi may have meant no license was needed, since many programs already get to use them as a windows feature... or maybe it did require some licensing. Either way Coyote may be able to answer better; the feature in PG products may have came with no licensing requirements for them to use this plugin. I hope you see what I mean by that.

FWIW Roland samples have been the basic soundset for windows for many years; I'm sure both companies have made a bit of $$ from this partnership.

As to "why include it?" - the MS wavetable, when used inside BiaB and RB (and PT) can be heard when played. It can be recorded as it plays .. but it can not do the 'render to wav' conversion. It doesn't have those capabilities to write the sound to a wav file. Seems like it should but it doesn't.
The Forte DXi module allows it to do this.
Another thing the MS synth can not do is be used on a track and then have audio processing effects after it; the DXi module from Coyote allows this feature also. Nice for the price.

I do not work here, but the benefits are still awesome
Make your sound your own!