Re: On the face of it
using 'Gnome shell' rather than 'Unity' probably cuts back on the level of effort they need to expend to get it.
It's not exactly 'vanilla' Gnome. That was the stated expectation when Unity 8, convergence et all was abandoned, that Ubuntu were going to go with vanilla gnome.
Then...a change here a change there, some to lessen the crossover for users now used to Unity, others, basically to polyfilla in some of Gnomes rough bits.