Point of order: the U.S. Constitution is very, very malleable – there's a pile of Amendments which make deep and significant changes to many aspects of the original text.

You can think of them like patches issued by government maintainers to the software of State.

Which, surprisingly, is very much like a hard fork.

(My personal and cynical take on why vests are use for witness ranking and not number of votes is twofold. Firstly, because account creation is relatively cheap for the amount of profit that you could theoretically expose by witness currency manipulation. Secondly, because going by vests privileges those who already have stake in the platform and the blockchain, to a degree which is almost unassailable by newcomer without bottomless pockets. This is also why the original design does not require re-voting on a regular basis because that would undermine the established order. Maybe good for establishing the belief in a less volatile value for a crypto-commodity, but not much good for pushing for anything but the original, classic definition of conservatism in the old guard.)