Modern HDMI-based systems can do this in one stroke. And by "modern" I mean that pushing my PS3 (yes, 3, not 4) button to start it up starts up my TV, and would start up my audio system were it not too old for that. (Though it occurs to me now to check whether it might do that if I routed HDMI in to it; for historical reasons I route optical audio to it which I believe lacks the channel for this.)
Shutting things back down seems to be a bit more challenging, though. The TV recognizes the PS3 turning off and returns to live TV (the last thing I really want it to switch to, but whatever), but the whole system teardown is a bit more complicated.
