According to Bitcoin.org, nobody owns the Bitcoin network much like no one owns the technology behind email. Bitcoin is controlled by all Bitcoin users around the world. While developers are improving the software, they can't force a change in the Bitcoin protocol because all users are free to choose what software and version they use. In order to stay compatible with each other, all users need to use software complying with the same rules. Bitcoin can only work correctly with a complete consensus among all users. Therefore, all users and developers have a strong incentive to protect this consensus.
Not necessarily "all" but rather a certain percentage, maybe 90% (I'm not quiet sure). This is what you called decentralized. This is a good thing since there is no central authority really to decide by itself to which path will BTC go. It needs to tell others and make them agree that this path will be where BTC is going.