git is decentralized, but the most common workflow makes it basically a slightly better SVN. There is always one authoritative upstream repo, and everyone just pushes to that. Really, GitHub + git is better than SVN in only two ways: better merge tools to make branches cheaper, and local branches. Almost everything else could already be done with SVN (or similar) before. git's decentralized nature is only really used by the Linux kernel developers AFAIK.
You can commit without pushing, and generally have full freedom to rearrange your repository locally. So no, lots of us make use of Git’s decentralization all the time, even without mailing patches.
