That's one of those common beliefs. In fact, when comparing an early MK2-Brompton from the late 80ies with a current one in detail you'll recognize that in fact there are only a small handful of things hat have NOT changed. The only two that I am aware of are the standard steel seat post - and the rear hinge. Every other part HAS changed, at least once, many more than once. Maybe I overlooked some constants but it can't be many. (Edit: I was informed that the seat post did indeed change over time. The second bit that did not change is the little plastic knob on the stem that keeps the folded stem in place /Edit). Considering that I assume that the design is considered to be not that bad and - as often - many of the people critzicing it do not fully understand how the thing works in terms of loads etc, (no affront intended), they just see a relatively small bolt and judge "bad design". Which is not how engineering works.