Bare in mind that HRT & Marussia do NOT have KERS in the F1 2012 game.
This is because in the real world F1 2012 season those 2 teams did not have a KERS package.
If you are using a PC, there might be a mod to add KERS to the HRT and Marussia teams, by doing a simple edit in the game database to switch KERS on for those cars.