some people based their entire bias on BiaB's free MIDI sounds, well actually they were a Microsoft GM set, and thus said MIDI sucks
Just as a bit of info, the MS GM sound set was licensed to them by Roland long ago, so they are actually a Roland set.
Much like the old VSC DXi synth (which had better samples), this sound set was cast aside by Roland (long ago after being 'dummied down' for the OS use). They continue to let MS continue to use it.
Also, this default set of samples can be tinkered with (within the OS), but as Mario pointed out; the basic free set that comes with Windows is from the W95/98 era and pretty basic. If'n you use your imagination you can almost here the intended sounds. That's Windows fault, and not BiaB.
/the more you know!