The cryogenics units and their occupants were not at all bereft of power, or artificial gravity though. Khan Singh showed absolutely no sign of muscular atrophy or any sort of physical malady at all. AG was maintained (out of necessity) for the duration of their voyage.
No sign of muscular atrophy? Why, Khan was barely able to pick Kirk up and toss him like a rag doll. If he hadn't been weakened by two centuries in microgravity he'd have thrown Kirk through the bulkhead and left a perfect little human-shaped cutout in the wall!