Yes, Dave, there is a significant difference. VI-14 Stac from the Basic Instrument set has only two velocities, mf and ff. (the crossover being at 88 to 89). Stac 1 and 2 from the Short-Notes folder have four velocities: p, mf, f, and ff. I assume that other instruments are thinned out in a similar manner, though I haven't checked.
I understand the crossfading argument (that you'll get phasing and other artifacts when one sample is superimposed over another). But my ears prefer that issue to the unplayability of the cross-switching of significantly different dynamic samples. So some basic instruments become more usable when crossfading is used.
I recently purchased the SAM brass bundle. SAM unapologetically assigns samples to maybe two to four keys at a time. And the sounds are perfectly usable.
Tony, I agree, especially with the trumpet. I think it's partly due to the significant timbral difference between a soft and loud trumpet.