Game covers are a big thing and they differ from region to region for a reason.  The NA MGS4 cover might work for Japan but that's a terribly cover for NA.  That isn't going to sell anyone who doesn't already know the Metal Gear Solid franchise and the fact it's the fourth installment is going to do even more to chase people away if they don't know the previous 3.

People might be willing to take a chance on a cover like that if it was just Metal Gear Solid on the cover, but Metal Gear Solid 4?  No, they would rather get generic shooter with the action cover (in NA at least).

Metal Gear Solid 4: Imagine they released a new version of Zelda, only they made Link a 50-year old sex offender. That's how most casual gamers viewed MGS4. You're a guy who used to be awesome, but now you're old and creepy.

Killzone 2: I'm amazed it's selling as well as it is. Top quality shooters are a dime a dozen on both HD consoles. The only TV Advertising for it was the 'guy shooting the other guy in the eye', which was just a big cinematic that didn't explain what the game was like or why it was cool.

Sonic: Really? You're surprised when "It's sonic, only also a werewolf, so you don't get to run" does poorly?