Quoting: MarlockPutting it plainly, you can plug a PC to a TV since forever, and all PC games are playable on a typical PC setup (monitor+kbd+mouse on a desk)... but a TV usually means a couch or bed instead of a desk and kbd+mouse doesn't really work on a couch or bed.

If the Steam Machine is meant to compete with consoles, then it's essential that Valve pressures for controller support in its games catalog to improve.

Just to be cheeky, if "forever" is about 25 years, then yea. In those early days, connecting to the TV was not seamless and it was frustrating to have a widescreen TV but only be able to get 4:3 resolutions on it. But, HDMI greatly improved the situation.

Have to say, though, that "kbd+mouse doesn't really work on a couch" was not the case for me. I set the keyboard and mouse up with extension cords on a wooden TV tray and had a great time (I've never been all that comfortable with controllers). Now, I game on a laptop. My comfort level with controllers is likely to change too, as I find they seem to help with the vertigo.

My spouse would never have tolerated my gaming in bed, LoL.

In all seriousness, though, I think that Valve really is targeting the Steam Machine as a console not a desktop PC.