I would have to think that Bryston is targeting an audience for this product that isn't interested in these details.
Seriously, most, if not all (myself included), couldn't tell the difference between a 24/48 and a 24/88.2, 24/96, 24/176.4 or 24/192 music file. A lot of factors have to be just right before this is actually significant. In reality, it's comes down to a marketing number. This unit has a higher sample rate than this other unit, so it must be better? Bryston seems to have decided the majority that would want this unit couldn't care, since it's not first and foremost a music processor. It's for theater and 48K sample rate is fine.
The web site tells us, this product is targeted at "high quality home theaters built for home cinema enthusiasts" and not for its music prowess.
Personally, I think Bryston made somewhat of a mistake in their naming of this unit. When you sell a unit called SP3 and then you release an SP4 model, this screams "upgrade path". Anyone with an SP3 decides their unit must be obsolete and it's time to look at the SP4. That just isn't the case if you look at the specifications. They're a different product.
Why did they not name the SP4 something like SP-HT?
brucek