Valve is sweetening the pot for Sony PlayStation 3 gamers who are interested in their forthcoming game Portal 2. Buy the PS3 version of Portal 2, and you’ll be able to download the Mac (and PC) version for free.

[ad#Google Adsense 300×250 in story]Portal 2 for PS3 will include cross-platform play for multiplayer games, cross-platform chat, and cloud-based storage of saved games – so you’ll be able to pick up where you left off in a saved game regardless of what platform you’re playing from.

Valve indicated that the PS3 version of Portal 2 will include the ability to unlock a “Steam Play” copy of Portal 2 for Windows and Mac OS X at no additional cost, if players link their PSN and Steam accounts.

“We made a promise to gamers at E3 that Portal 2 for the PlayStation 3 would be the best console version of the product,” said Gabe Newell, co-founder and president of Valve.

The news is a shot across the bow of Microsoft and its Xbox 360 console. Valve has been unhappy how Microsoft manages its Xbox Live service; Microsoft required Valve to charge for downloadable content (DLC) for its Xbox 360 version of Left 4 Dead 2, for content that was given away for free to users of the Mac and Windows versions.

Valve indicates that Portal 2 will be released for the Mac, PlayStation 3, PC, and Xbox 360 this April.