As already posted by others, on NAmerican routes it doesn't make much difference to AC as it is already filling its seats without the extra leg room, and AC has always had better pitch than US carriers and most of its other domestic competitors. Taking a row out to add another few inches to the first four or five rows would only reduce capacity by six seats. Would you be willing to pay more to make up for these missing seats?
Parnel has speculated that AC's new configuration on international widebodies may contain a mid-class cabin that does have more pitch. We'll have to wait and see. I think these are really the only routes where this can be justified, but as someone who does still fly in the back on transAt and transPac flights from time to time, I have never really found AC's pitch to be a problem, unlike some airlines -- BA, LH and IB come to mind from past nightmarish flights crammed into the back. I'd rather see better IFE on AC in the back before another inch or two pitch.