Besides, you couldn't hit the side of a barn with the side of a barn while moving back and forth with a scoped weapon in real life. Another cool thing is the ability to lie down to fire. Going prone improves your accuracy and reduces your exposed body parts. The trade-off, obviously, is that it takes a second to get into this position and get out of it. It's just the coolest thing to see a sniper, slithering around a corner in the prone position, take aim and separate an enemy's head from his shoulders at long range.
Realistic weapons do realistic damage, too.
No longer will you be frustrated after putting multiple rounds into an enemy to only see him run away to fight again another day. One of my favorite weapons is the Claymore mine. Lay this baby down and completely shut down a hallway or command point for a short period. It's humorous to see people run from the little green blob on the ground. Now, if only you could specify the direction you wanted the thing to point, that would make it a truly effective weapon for the ambush.