If we ever do see an Android OS update, it will most likely be the last. The Cell phone technology is moving so fast, it's not worth their time and money to spend any more time on this. For every customer that gets upset and goes to another brand, they gain someone from the opposite brand.... It causes very little impact to their over all revenue.
It gets to a point where it's not cost effective to continue to support legacy products (know matter how new they are) and are usually willing to risk the loss of a few customers, in today's market they will gain probably more than they lose for the next new cool device.