Capcom has released an official statement in response to the uproar over Resident Evil: The Mercenaries 3D single, non-erasable save file:
'In Resident Evil: The Mercenaries 3D, all mission progress is saved directly to the Nintendo 3DS cartridge, where it cannot be reset. The nature of the game invites high levels of replayability, encouraging fans to improve mission scores. The save mechanic ensures that both original and unlocked game content will be available to all users. Secondhand game sales were not a factor in this development decision, and we hope that all our consumers will be able to enjoy the entirety of the survival-action experiences that the game does offer.
There was no intention of lessening the experience of the game. Essentially, RE Mercs was treated like an arcade fighting game. You unlock characters, levels, etc and they just stay unlocked as they would in an arcade machine. There was no hidden motive to prevent buying used copies. It's not some secret form of DRM. It's simply the way we designed the save system to work with the arcade type of gameplay.'