Does this mean the people who buys the PC version will get the PS3 version for free?
No, sadly, it doesn't work the other way. (Well they haven't said it will anyway) I suppose they could do this but I think Sony would expect to be paid for each copy made. It costs valve little to nothing to unlock the game for accounts linked to PSN accounts so I don't think Valve cares about giving ppl free copies on the PC as long as they purchased something valve gets money. Well...they don't care about giving PS3 owners free copies on the PC...PC gamers need to still pay just cause.
It would be pretty awesome to see them give Portal 2 away for free on steam to everyone on the PC...that would...wow I can't even tell you how many publishers would shit their pants at that.
It would give Valve and Steam ABSURD leverage in marketing to the PC gamer audience as EVERYONE would gladly jump on board steam to get that game free and then you look at the other publishers and Grin...so you guys wanna sell a PC game hunh? Well I can sell millions of copies if you give me $20 per copy, or you can sell far less, make less money in the end, and not use me...and I'm your competition so that can't feel like a good choice either way hunh?