Gary
You said "One thing to realize is that manufacturers are going to build in obsolescence into these motors They wont be the same as motors of old. 2000 watt motor will spin at about 30 000 rpm were as a 500 watt motor about 10 000 or there abouts, The lower the wattage the slower the motor the longer they last. That's a issue for the manufacturers."
In the theory, I would back you all the way with this. In the practice, and speaking only of cleaners I have known about here in the UK, motor failure is not one of the main reasons why people here are disposing of cleaners at the moment. Now I admit quite readily that I have no figures to hand, but it seems that aside from Dyson, most other vacuums purchased are from the much cheaper end of the market, and it only takes a drop in suction, a broken part or hose, even a belt, and people here are throwing out their cleaners.
As you quite rightly say, the newer motors are liable to last longer, but for me I think that today's cleaners already contain enough 'built-in obsolescence' to more than compensate for the length of time the motor will last for. The quality of our cleaners is dreadful - at any price.