I've also read that modern high speed lifts are only expected to have a 20 year life.
I believe this has more to do with regular replacement cycles in France because of the regulatory regime in place there.
In terms of keeping older lifts going, Kirkwood, CA major front chairlifts are now 43 years old (older than the Ciste Chairs on CairnGorm) and will continue to be in operation indefinitely. One of the original Yan Triples, Chair 6 (Cornice) underwent an in-line upgrade to a high speed quad in 1999 and is now in it's 16th year of operation. It wont be getting replaced any decade soon! If you hammer the lift at full pelt all the time things will certainly need a lot more upkeep and replaced a lot more frequently, big difference in running a high speed detachable at 6m/s flat out and 4m/s which is still comfortably more than double a fixed grip.