After posting this I started wondering if part of the Centurions' desire to be 'human' was some sort of memory of having been flesh, thanks to Zoe Graystone's avatar-self (complete with all the information Zoe had given her) being a starting point... Yeah, I watched the first two or three episodes of Caprica, so that's the theory I'm left with from seeing that much of the show.

Human bodies have the whole sense-interaction thing that metal doesn't have, even if they're programmed to hear, sense temperature, etc. Hm.