If I'm remembering right, Shuttleworth decided to go his own way because at the time Gnome Shell looked radically different than it does now, and he didn't fors

If I'm remembering right, Shuttleworth decided to go his own way because at the time Gnome Shell looked radically different than it does now, and he didn't forsee it--or the political environment around it--improving enough to bother building upon. However since he made that decision and showed some Unity prototypes, the Gnome Shell design did change a lot and now it resembles Unity much more than it did back then.