Yes, but that doesn't mean it is decentralized. In fact, centralization of mining power is one of the biggest concerns for BTC now. Further, I don't think BTC protocol allows rollbacks.
It's decentralized if no one entity has 51% power (or 90% when TF is implemented in a few months). There is no one entity in NXT that has 51% forging power. If forgers decide to download the modified release and do the rollback, then it's democracy in PoS style. BTC software could also be modified to do a rollback and if enough miners download it and reach 51% of mining power OR if enough miners decide to secretly mine a separate chain and reach 51% of mining power, they orphan all the other miners' blocks.