The heavier use of CPU allows the files to be smaller while retaining quality (or vice-versa).
As all current platforms, including mobile because of dedicated hardware, have absolutely no problem with playing H.264 video while bandwidth is still a scarce resource I think it is logical and wise that H.264 won over MPEG-2 or other older codecs.
Don't forget that larger file size also might mean more power consumption (storage and radio need to be active longer) even if less CPU is consumed.
As all current platforms, including mobile because of dedicated hardware, have absolutely no problem with playing H.264 video while bandwidth is still a scarce resource I think it is logical and wise that H.264 won over MPEG-2 or other older codecs.
Don't forget that larger file size also might mean more power consumption (storage and radio need to be active longer) even if less CPU is consumed.