Wave was certainly not developed by a hundred-person team. That article says that the "enabling technologies" behind Wave, including GWT and Google's XMPP fork, comprise a hundred-person team, which I could maybe believe between three or four of Google's key infrastructure projects at the time.

I think in Wave's case, as an innovative technology that had no clear predecessor, most of the two years is probably design, not development. Wave missed its mark, so none of that design is really re-usable.