I dont think Linux mint will continue in sync with Ubuntu for long time.they may sync their packages with Debian repos may be.
Simply Mepis tried a release with Ubuntu base,they quickly repended(warren) and went back to Debian Testing base
Ubuntu is simply very fast in development,their Gnome,other packages all are now not from Debian Sid any more.
linux mint bundling codecs-the legality may be a issue in usa and all