The embargo is typically an agreement between the publisher and outlet, and it seems Gearbox was ready early enough for 2k to leave some wiggle room. The rest of the outlets won't publish until either the review is done or on a publication schedule.
"A large, fast moving fire is the only thing that would make anything on MTV watchable."-- Reel_Big_Mike
If there was NO embargo, I guarantee there would be at least 20+ reviews right now. Sites like Gamespot, 1up and online mags have had the game since late August. As did IGN and GI. IGN actually get first priority on reviews because they advertise games for less money.