AlphaGo is impressive no doubt but has DeepMind done anything really key to Google's bottom line yet? A lot of the really sweet stuff they do doesn't have immediate commercial utility that I can see. Apple might be waiting to strike once Google has found the killer app (remember they're never really first at anything and focus holistically on the product).
Apple is benefiting from other companies releasing their research. If everyone but Apple releases the community is nearly as good, and Apple gets the pick of external and internal research while not needing to give up any of their own ideas. I know they send people to conferences and it can be a bit weird talking to someone who won't tell you anything about what they do.
Regarding researchers, I don't know of any top trend setters who've joined but they do have some very good applied ML people through direct- or aqui-hires.
Tl;dr: Apple doing what they usually do and keeping their powder dry/free loading off other's work until they can execute the product.