That's an interesting assumption. The switch from GTK+ to Qt isn't only a switch from a GUI toolkit to an expansive UI and application framework, though that is hugely beneficial, it's also intended to speed the development of both Maemo MeeGo itself and the applications that run on it.

Maemo hasn't just used GTK+; it has used GTK+ and Hildon. Up through Bora, the system used a forked, highly customized version of GTK+ 2.6. Going it alone on that got to be too taxing, and so with Chinook, Nokia broke backwards compatibility of Maemo and based Hildon 2.0 on GTK+ 2.10.

Again though, Nokia's finger friendly, touchscreen oriented changes weren't always accepted upstream, so they found themselves continuously having to adjust and reapply their patches to the rapidly evolving upstream GTK+ code. That work consumed resources that could otherwise have been used to move the OS forward.

Harmattan maintains much of the Gnome software stack, but switches to Qt as the primary toolkit to get away from the problem. Meanwhile, Nokia did contribute money to the Gnome Foundation to have Igalia work on integrating bits of Hildon into GTK+ upsteam for GTK+ 3. That should help with porting GTK+ 3 applications to MeeGo.