Long Rifles are more like a RL Battle Rifle than a RL Sniper Rifle is what i am getting at. SD downplayed sniping. while you can slap a scope on a Long Rifle and snipe, it isn't as effective as a realistic Sniper Rifle. for most shooters, the lack of a sniper would svck. for most games, snipers are to easy to manipulate. for Brink, the lack of snipers works out pretty good.
While there is now a market for what are deemed "Sniper Rifles" like the Barret .50 cal and similar weapons, that is a case of manufacturers specializing in the making of an item, and not a case of the item needing to be specialized. A sniper rifle can be any high precision rifle fitted for "extreme ranges".
But for the purposes of FPS gaming the argument is unneccesary as the "long/light rifles" are simply descoped sniper rifles which we can then put back together again. There will be no lack of snipers, but due to the smaller numbers involved in the game and the objective-centric play there also won't likely be an over abundance. There will, hipefully, be the right number of skilled marksmen.
And as EASy88 noted, the Barnett is more than enough rifle with which to snipe.