I like to think of it more as partial stasis than complete stasis. Remember that the Emperor had to give Dorn instruction to modify the golden throne and make it into the life sustaining machine that it now is. If it was simply a matter if being a stasis chair, than when it was discovered that the golden throne was failing wouldn't the AM be able to do some sort of repair on it?
Now if the golden throne wasn't just keeping the Emperor in stasis, then that might mean its doing something beyond the AM's means to comprehend.
As far as the Emperor's appearance; never forget that the golden armored warrior/god is supposed to be something of an outward projection. Considering everything that happened to him during the final fight with Horus, his energy would certainly not be well spent maintaining an image of himself. So maybe he always looked like a nondescript frail man, but projected the image of perfection because that would be easier to follow.