Well, yes, but when using "to hit" modifiers you notice that each negative one effectively lowers your BS by one. So, if BS value is 3 and above mentioned modifiers comes to play (range, cover, movment), BS is 0 (3-3=0) and you cannot shoot. That's how we play. It even makes sense - imagine a warrior who barely sees his enemy (long range and cover modifiers), who's on the move and has no chance for standing still and aim precisely (moving modifier). He decides that his shot will be wasted, so he saves an arrow/bullet for a better occasion.