How old are you? First of all, who are the top 3 players in mpg this year? Just like we all expected, it's the superstar trio of Rudy Gay, Luol Deng and Nicolas Batum.
Your post makes absolutely no sense. The reason superstars don't get tired is because the stamina rating is not scaled down to match shorter quarters. This applies to any other player, too. But if you can run in circles holding turbo for full games, people like to do this with an overpowered star superman instead of Nick Collison. In theory, you could do this with anybody.
Seriously? You compare the gameplay of 2k13 to the real NBA? Fine, let's see...What's "real" about players sliding on defense, unstoppable canned dunk animations, signature skills that boost your team's attributes after a dunk, lack of defensive contact, overpowered spin dunks, self-alleys and iso moves?
If you really want to play the realism card, let's just say that even Kobe and Durant don't dunk more than 2 times on average over the course of a 48 min game. So basically dunks happening more frequent than that "is simply not how the NBA works". Would you like that? Running straight into you defender until a big man helps out resulting in a lead pass to Griffin and Howard, holding turbo everytime you bring the ball up court, chaining iso moves without losing momentum...2k13 is NOT about real basketball.
And the reason you can exploit superstars online is that a lot of kids playing the game know exactly 2 things about basketball: 3pt-shots and dunks. That's it.