I don't see this as being any different from what Microsoft has been doing for 20+ years. They let a competitor put the work into figuring something out, then make a a reasonably accurate facsimile thereof. I think it's lazy, but not particularly unethical. If Google were Benz, would they be complaining that Ford was making 4-wheeled vehicles with an engine? More appropriately, and given that I've been on a Top Gear bender lately, if Google were Cadillac would they be complaining that everyone else was copying their method for operating vehicles, with three pedals, a gear shift, a steering wheel and a handbrake?

I get why Google is upset, but this doesn't strike me as unethical behaviour in a free market.