Uhm, the PD also has large amounts of crit. Basically AD carry's DPS consist of AD times AS times Crit.
In Corki's case, he spams spells too inbetween attacks and has AD ratios on his abilities. Therefore he tends to focus more on AD and crit over AS.
If you were so worried about the nerf, you could take bloodthirsters instead of IE's crit focus. However, your endgame damage would still suffer. Obviously multiplying 3 things together is gonna be stronger than just 2 things multiplied. 4x4x4(64) is a lot bigger than 6x6(24) even though the total sums are the same....if that helps visualize.
I'd recommend TriForce for Corki. His style works well with it and it gives him much of the PD advantages (movespeed, some crit, some AS), while giving tons of other stuff (AP, health, mana, AD, the slow onhit, the ridiculously good damage proc)