I could be wrong, but I believe that they will replace that part even if it out of warranty because it is a defective part.
I had mine replaced (it was great, they replaced the whole top piece, which includes the keyboard and trackpad), but I can't remember if I was out of warranty or not.
It's worth a call to Apple to see if it is covered. Mention that you believe it is supposed to be covered, even after the 1 year warranty period.