Think of it like this: if you use up all your innings in, say, August, you're WAY ahead of all the others in Ks, Ws, and (hopefully) ERA and WHIP. ERA and WHIP, maybe those are safe, unless you deal your good pitchers to teams that then use them to catch you. Ws and Ks are another story. You may think you're "uncatchable" but you forgot that you won't be striking any more guys out and your opponents still have 200 innings with which to work. And wins are so unpredictable that you never know what will happen there.
I'm not saying that the strategy has NO chance of working, just a small chance of working. It's too hard to predict what others are going to do over the last couple months of the season to ever think you have all categories locked up. Plus, like said before, you lose all your bargaining power by not having any innings left. If the other guys are smart at all, they'll speak with each other and come to the agreement that they won't pay a ton for your pitching knowing that you can't use it.
Just my two cents.