i think it has to do with braking, more than accelerating. on a start, all bikes feel slippage. on a stop, you'll feel even a slight loss of traction through your legs/whole body, and not just through your (perhaps numb) fingers on a brake lever. i would also speculate that modulating braking force (to find the sweet spot between slowing and slipping) is easier fixed in the winter, due to cold/numb hands vs legs, and not having to deal with wet rims (unless you run disc brakes).

maybe?