You're not losing as much as you might intuitively think, if you look at the ranges of the physical instruments. The lowest note on a violin is G above middle C (C3), so you're losing only 5 semitones off the bottom. Generally speaking, cellos cover that range in a more pleasing way than violins anyhow.
It's common practice for libraries of this type to switch instruments in and out based on note values, purely as a convenience for quick 'n dirty orchestration. Most casual users don't know or care what the ranges of the actual instruments are, just whether it sounds nice. SI Strings and similar instruments are not meant to be a substitute for a proper string library, which would allow you to exploit the full range of each section. Sometimes, you want to intentionally have a bass play something at the extreme high end of its range, for the peculiar tone the instrument gets up there. But if all you want to do is lay down a string pad behind a pop song, you just want to easily achieve a pleasant sound without regard to the intricacies of orchestration.