The only two uprights I have with variable suction are my Miele S7510, and Sanyo SCA-7, which is a fair few years old, and a re-badged Panasonic of that time period. The Miele S6 is a very good canister for variable control, but has an adverse effect on the turbobrush rotation if the suction is turned down too low though. I think that one of the reasons why uprights dont have the power control is that most have only one motor for the suction and it drives the brushroll as well. If the power is reduced then the brushroll will spin slower too, possibly becoming jammed or stopped easier which would damage the motor. The S7 has a seperate brush motor so this spins the brushes at a constant speed regardless of the power of the suction motor. However - the lower power is only usually needed when using the tools so I cant see much of a problem in that respect.
Dyson dont offer power control on any of their canisters and some of the more budget range canisters dont either like the VAX essentials range.
The Henry has 2 speed motor control, but cheaper models like the James and the Basil didnt, and in the Henry, this autosave feature has only come about recently. Before 2006, I think even the Henry was only 1 speed.
I'm sure penny pinching has a lot to do with it as many companies are going this way since the recession to cut costs and maximise profits. Look at the Hoover TP1 compared to the Ranger or PowerPlus - after the recession of the early 80's, Hoover needed to cut costs so produced cleaners a lot cheaper in quality with all plastic and very little metal.
Incidentally, not many dirty fan models had power control - it was only something that appeared on the later clean air models after about 1983 starting with the famous Hoover sensotronic - now that was a cool cleaner for gadgets and lights.
