Meh, it's a timed thing. You still get it if you don't preorder, you just have to wait a month. Also, it's not like it's expclusive to Gamestop or something. (or is it?)
I do see the point there, but for me it makes a huge difference. Preorder bonuses should never ever be content, even accelerated access to content. That's not a bonus, that's a penalty for not giving retailers an interest free loan. I'm sure it seems like a silly thing to be against, but the implication is that you're artificially receiving less functionality (even if just for a while) for the same price. The dollars you pay for the game pay back the development costs associated with making the modes but you can't use them for whatever period of time, possibly because you believe in the time value of money.
Locking access to a mode like that is pretty similar to, say, Honda locking access to your windshield wipers for a month because you didn't use their financing. You paid the same price, you should get the exact same core commodity. Now, should this mode be a beta test of a future download or something initially, then fine, that's reasonable; early access to a "service" not part of the core package. Locking out users of a service, however, is just plain wrong. And, if that service is advertised on the box it could lead to trouble.
"Bonuses" like this need to be stupid things that don't actually matter - you know, bonuses. Gold carts, t-shirts, hats, shit like that. Not things that actually affect the product itself.