Bench press form is different for bodybuilders/powerlifters. You should state which one you're going for before these arguments get started xD. If your wanting to build muscle I think your back should be mostly flat.. Time under tension/rom will build you more muscle then pressing alot of weight 2 inches. (no offense to any powerlifters)
Exactly. I mean no disrespect to power lifters at all. Its just not my gig at all and neither is the bench for that matter. As a bodybuilder, I try to focus on targeting a muscle group (chest), so putting the whole body into a movement is not what I'm after at all. Actually I've abandoned bench altogether for a good while now just because there are so many better exercises to isolate the chest for growth.
From a power lifters perspective I agree completely with you guys, when achieving maximal force is the goal.
Good discussion here