For a "gaming" keyboard, the only rollover that matters is 6-key in the QWEASD block.
Huh? Only if you're just going to play certain fps games and not fiddle with the settings. It's probably a decent starting point for low-end gaming keyboards but if it's going to be branded a gaming keyboard then it really should shine in all games.
Racing games for example use the arrow keys. Try holding down a vertical and a horizontal arrow key and pressing 0 on the numpad. It doesn't show up on my model M so I'm pretty sure having n-key rollover there would be beneficial too.
And then there are spaceship games than use WD for acceleration, the surrounding keys for functions and the numpad for steering.
Any top-end gaming keyboard should allow any combination of keys I can actually press.
EDIT: I've had a similar deal trying to get the rollover information of the Cherry G80-3000. I emailed two companies that sold them, one told me cherry had told them that the G80-3000 had full n-key rollover but they hadn't tried themselves. The other told me that cherry had told them that the G80 didn't have n-key rollover because adding the diodes would push the price up. I have sent an e-mail to cherry over the weekend but I haven't had a reply yet.
Unfortunatly this kind of blatent lying is pretty much everywhere in the PC market. Apple's recent "Thinnest Laptop" claim is a good example but there are many, many others.