Neil McGovern writes in an recent email: "Following the plan outlined in the previous release update, we are now in deep freeze, which means that we'll only be migrating to testing packages that fix RC bugs." A deep freeze is one of the last phases before a release of Debian. There is lots of bug fixing and documentation still to do and you can help. Check out the New in "Squeeze" page for example; and if you find bugs in the installer help report and even fix them.
So, if you are not getting many updates in your LMDE for a while, this is probably why.