Since the announcement of "Steam Play" I've wondered if this will ever cross onto the console side, where you buy an Xbox 360 or PS3 game and it's also playable on PC or Mac, most likely through a download code. Similar to the Digital copies of movies available in most new blu rays - dvds. With downloading clients becoming more and more a primary source of distribution it would make sense and would be really awesome.  
Just a silly fools dream?

That might be a little too much to ask. Within Steam, everything is under Valve's control, where as on the console side, you have to deal with Microsoft or Sony. Since most games will come with online play, their going to want the customers to play on their servers...

I'm pretty sure it's against a terms of service contract they sign when they get games published to disk because of all the things to do with packaging requirements. But that's not to say that Amazon or someone else with download codes for both can't do a "Buy one, get another" kind of deal for their customers.

While that would be amazing... I doubt it will ever happen.

I doubt it. They still make plenty of money without offering this kind of deal.

The release of console games is controlled by the console manufacturer. If they don't approve, it simply can't and won't happen.

steam play is only for valve's own games anyway, which makes sense, since they can't expect any developer that distributes via steam to port their games to mac.