Yes, being Yoga as Relaxation Technique , the practice of it reduces the Body?s consumption in daily routine. The sound sleep obtained through Yoga can give peace of mind.

I would agree to the point that it's probably not doint Asanas alone what is decreasing the amount of sleep - it's more the yogic (or any other form) of meditation which does so. It's in meditation where you go in the most subtle aspects of your being; levels in which your consciousness (or unconsciousness) travels during sleep.

From personal experience, yoga may give you better quality sleep, sleep moves in 1.5 hours cycles from memory, we become more aware of cycles as we grow older. Deep meditation and relaxation can also reduce sleep required.

Having said that yoga is just not the physical aspect, a lot of the eightfold path reduces stress allowing you to sleep better, and meditate better.