I have to admit I'd never really given this too much thought. Mr Boeing says don't chuck the flaps out >20000', so I don't. However, BelArg's post got me thinking (which is not pretty at the best of times).
We know we don't put the flaps out at too high a speed because they will get damaged by the number of Bernoulli's hitting them (I like to keep things simple in my mind
). The higher the speed, the more Bernoulli's. Now, we also know that the only measure we have of the number of Bernoulli's in the air is INDICATED airspeed. So, given that, why would a manafacturer either put an altitude limit or a mach number limit on the flaps? Surely you can just stick with an IAS limit because that will measure the Bernoulli's in the air no matter what your altitude.
It obviously doens't really affect the price of fish. I'm not going to use the flaps that high and I have no intention of chucking them out too fast but I was just wondering why they just don't stick to an IAS limit and have one fewer line in the limitations chapter.