Yeah, but at least the XBOX sits in a low power mode that does updates and keeps the spot you were in your game saved. It's really transparent. I'm not saying Steam can't do that but it's not in the same league yet.
Steam does exactly that for me, thought when I'm casually using my computer, not when my computer has gone to sleep. But since Valve controls the whole steam machine ecosystem, I'd imagine it would be possible for the steam machine to do the same sleep-updates as xbox