The need could be explained to be used to play such games with a gamepad. I found it hard to play AC2 without Gamepad and as such stayed with it. Same goes for Legend of Dragoon, I'll play it with Pad instead of keyboard (I'm emulating this).
Bioshock or every other "shooter" like skyrim, fallout or such I see better with Keyboard Mouse as I suck at aiming with a controller.
I've got F.3.A.R. at christmas for the PS3 and well... I played the prologue on easy and wasted ammunition on the first guard you try to kill there and even with bullet time and such stuff I died in a room where you are forced to rush into. Normally such shooters (like Quake 4) I play on at least Normal (or the next after normal).
Those buttons are not necessary as long as you configured everything else in a good way. My Mouse-Extrabuttons only were for the Grip and for the Gun to change between these two. The part you mentioned... let's just say I needed a few tries too, just memorize that part. Good Luck.