That's fine if the only devices you're controlling are your TV and cable box, but take a look at this:
To watch a DVD in my setup you need to:
1. Turn on the TV.
2. Change the input on the TV.
3. Turn on the Pre-amp
4. Turn on the AMP
5. Turn on the DVD player.
6. Turn on the video processor.
Now you have a problem, because your movie functions are controlled by your DVD player, but your volume is controlled by your Pre-AMP. So if you want to hit "PLAY" it would actually have to be "DVD" then "PLAY", and then if the volume is too high/low you hit "Pre-AMP" and "VOLUME UP/DOWN".
I can only imagine the conversation when I'm at a dinner party and the 14 year old sitter wants to watch TV