Yeah my old cable provider and DirecTV which I currently have charge more. I think for Cable it was 10 bucks like you said and DirecTV doesn't offer SD as far as I know but charges you an extra 5 for HD boxes with no DVR
Don't worry, the "premium" will vanish with time! Remember, what first flat panels used to cost? Yes, the 32" plasmas? I bet 4k will fall much faster than those did.
PS 4k panel in a 55" TV has the same visual effect, that Retina screen on Apple's devices. It's just not marketed like that.