75% is generous, normally you need 67% to change constitution laws in most countries. It is always tradeoff how big minority you want give the right to veto majority will. If you think 5% or 10% can veto 90% majoriy, your probably part of this minority and want more power than you actually have.
Bitcoin is not a political thing (so trying to compare it to such things is just plain silly) - it is the fact that Gavin is trying to treat it that way now that is the issue.
Miners do not want to face risks of not being able to turn their BTC into "fiat" because it actually costs them a lot in electricity bills to keep mining (which secures the network).
If we end up with too much doubt as to what is going to occur then exchanges will stop allowing fiat to be exchanged and miners will be forced to start shutting down mines (due to the expense of running them).