The same question came up with my brother and father and I this weekend and we concluded it is balance and the guy is just uncommonly light on his feet.
I hold my breath every damn time he has the ball. It's involuntary. His style freaks me out.
The little guy looks like being seconds away from career ending tackle, all the time. Unbelievable elusiveness, motor skills and balance. The big clumsy linebackers make a mess in their pants as they see him get the ball.
Tate's hands are really sticky. That aspect of his game is under appreciated compared to his elusiveness. He had 2 drops last year (49ers) and no drops in 2011.