When the Rezound gets ICS, the 3 ICS buttons will also be there too. Doesn't that make the Rezound capacitive buttons redundant and unnecessary? Why have two sets of buttons that basically serve the same purpose?
Where did you get that information? The last I heard ICS would be able to tell if the phone it was on had capacitive buttons or not. If it had buttons then you wouldn't have any on screen buttons. Please post the link if you have confirmation saying the opposite.
I'm guessing he's speculating incorrectly, because it would be stupid to waste screen real estate when there are perfectly good buttons sitting on the bottom of the phone. (That I feel like I'd prefer more than on-screen buttons)
I know it has been stated multiple times that the capacitive buttons will replace the software buttons. Do a quick google search for "ICS capacitive buttons" and the first link that pops up will answer this definitively for you.
Using ICS on my Incredible, no, they don't stay there. If the phone has capacitive buttons, then the software ones won't show up. Don't know why you would think they'd be there.