I wonder if Google could respond by conditioning their search on the incoming requester's address. Either send garbage, or refuse and log.
I doubt it. If they tried that, it would slow Google's famously-quick searches considerably, surely have some bugs and lock out a few users, and take a significant amount of resources to execute.
And, above all that, M$ could just proxy their bot, foiling the whole scheme, and both would be thrown into a game of hide-and-go-seek, which would be counterproductive for BOTH sides.
Typical M$ behavior, IMO, but, AFAIK, technically legal. Oh, well...I'm sticking with Google.