Well a "better" rifle allows you to engage at longer range Fireteams tend to have designated marksmen with Battle Rifles these days.
Also a better rifel is less prone to jamming (this is why SF's prefer the piston version of the M4)
Also a better rifel is less prone to jamming (this is why SF's prefer the piston version of the M4)
Snipers are force multipliers ~ http://en.wikipedia.org/wiki/Force_multiplication