if you're going to go that far to say that base AC should be 11, you might as well just change the rule to say that one has to roll above AC to hit, not at or above. Then AC could stay at 10 and you truly get a 50% chance to hit.
I'm not saying it *should* be 11. I was just responding to GBDeluxe who said that a 50% chance was impossible to create on a d20. Had it been 2d10, he would have been right.
