This has been asked many times, and the answer is always the same (it was the same in this thread too, I think though LandLockedPH misinterpreted one of the replies) - ICS does not lose the ability to use hardware/capacitive buttons. Just look at the Nexus S (no on-screen buttons, capacitive buttons are still use) as well as the CM9 and other ICS ports to other phones that do have buttons.
There is an option in the source code to turn on the on-screen buttons, but the sane default is to disable the on-screen buttons when there are hardware/capacitive buttons present. It wouldn't make sense otherwise...
And again if you don't believe me, look at the official ICS for Nexus S.