Here's an example of how a Rockstar Games game can sell when no platform is shown preference.
Red Dead Redemption:
360: 5.09m
PS3: 5.02m
Undead Nightmare(Standalon expansion/dlc)
360:0.88
PS3: 0.95
Main game + DLC combined:
360: 5.97m
PS3: 5.97m
Look at that! It's a tie! An extremely successful new IP without any timed-exclusive content for any platform. No one gets screwed over here, everyone is happy. Take notes Activison/EA.