The two conferences have different kinds of players. The Big Ten has slow big guys and the SEC has fast big guys. The talent may be the same but there's no substitute for speed. Another factor is weather. In the Southern states football in general can be played outside just about year round. In the North from late december though early April it's just too darn cold to play outside.
In the North you need the extra bulk/fat to protect you from the the elements. I bet if you take a fast kid from Florida or LSU and have him try to play football outside in late november in Wisconsin or Michigan he will be much slower. And you when get hit in the cold it hurts like hell
So there you have it. Warm weather lends itself to more football being played and the game is faster as a result. The cold weather lends itslef to having more meat and bulk to deal with the elements and the guys are slower. A guy from the South could not tolerate too many games or practices up north and a guy from the north would sweat his butt off and be very uncomfortable playing in the south.
But as an argument, if born and raised in the south this lends to a faster more athletic type of football player. Talent level may be the same as the guy from the north. Funny though how they adapt after they get to the NFL.
Of course I could be wrong.