I don't buy that argument at all. There's nothing "realistic" about the CPU deciding when your player's gonna dig in and hit that next gear.
Besides, hitting the sprint button doesn't mean your player instantly accelerates to his top speed.
Like I said above: It's all about control, control, control. And auto-sprint doesn't give me that.
And lastly, to me it's just more fun to use the sprint button. It's like an extra move. I feel like I can set up slow defenders by running at 3/4 speed and then blow past them.