Wow. Calm down everyone. I believe the original intent of the XP cap was to prevent exploiters from being able to achieve max rank online quickly. With a cap, even if an exploit is found, it will take a while to rank up and give 343 a chance to fix it.
Just think back to the days before the seemingly untouchable, sacred "X.P.!!!!". If you are playing the game just for XP I don't care that's your choice, but it's really not that big of a deal and I am sure not many people are selling their copies of Halo 4 in fits of rage due to hitting a daily XP cap.