RTM, or Release to Manufacturing, is the same thing as the final release for Microsoft products. That is not to say that updates won't happen. In the case of IE10, if any updates are needed, they will come through the Windows Update process.
General availability is when the file gets pushed through Windows Update which is only happening now for people who were running the preview version of IE10. It will be offered to all Win7 users in the coming weeks. We just got a head start on it.