It's a fair physics question. A deflated ball has less air in it, and hence slightly less mass. Since F=ma, given equal effort (F) by Brady, a deflated ball will experience a greater acceleration, hence will attain a greater velocity, during the throwing motion. Furthermore, a deflated ball will presumably be a bit narrower and hence have different aerodynamics. I'll leave it to aero experts to chime in on this aspect, but less turbulence would likely lead to more consistency, hence accuracy.
That being said, I believe that the advantage Brady was after is indeed related to grip and comfort, and that the effects I describe above are probably negligible.