I would disagree with this, the total amount of bitcoin to be mined could easily be changed if they decide to tweak the code in the future. In theory it could be an infinite amount.
That could be the case if the protocol became the plaything of a small number of big players who try to dictate what's what. They may also find that they're left with something worthless when their helpless users run for the exits or ignore the fork and stick with the old plan.