Ubuntu Plans To Stick To "Stable GNOME"
Phoronix: Ubuntu Plans To Stick To "Stable GNOME"
Ubuntu developers will be looking to stick to "stable" GNOME components and not closely track the unstable GNOME development releases within the Ubuntu 13.04 cycle. There's several reasons why Ubuntu will be distancing itself from the latest upstream GNOME packages...
Err, this all boils down to 1 single issue
Ubuntu has forked away from upstream gnome, and the more changes they include the harder it is to keep syncing. It's exactly what everybody said would happen.