I wasn't as clear as I should have been... I'm just wondering whether it is a LA departure speed to get you moved out of the way or a Center-imposed speed because they need 280 (read "slower than usual") for in-trail farther down the line. I'm leaning toward the latter. I do understand that they're giving you a hard speed of 280 rather than telling you not to exceed 280. Sorry I didin't make that clear.
Dave