No, this is a common misunderstanding - developers don't possess any power except that of nomination.

The network has to come to a consensus about any change in rules. The developers could change the client to change one of these rules, and people would vote by using that client, or keeping the old one (or forking the old client to keep updating it without the rule change). It's actually happened before.

Your client will reject any block chain that doesn't conform to the rules as it understands them - so a massive change in rules will simply fork the blockchain into two different chains, obviously with the most popular chain being the one people use but it's entirely plausible to end up with two distinct networks that started out as Bitcoin itself.

So there's pretty much no incentive for the developers to make such a drastic change to the rules unless it's obvious the community would be 99% behind them. So everyone who tells you "well the developers hold all the power so it's not decentralized" doesn't grok Bitcoin at all.