Isn't compliance with robots.txt more of a voluntary thing?
I'm not accusing MS of ignoring it when convenient, but if you/we/someone is accusing them of acting unethically wrt search results in the first place, telling the crawler to ignore robots.txt wouldn't be that far away, would it? (And likewise faking the user-agent, etc.)
For better or for worse, UA identification, robots.txt compliance - all those things are voluntary. I'm not suggesting they shouldn't be, but it certainly makes a difference in terms of whether something's possible or not. (And, if you ask me, places an even higher obligation on the actors to behave ethically, lest trust completely evaporates and the whole thing goes to hell in a handbasket).
It would take a pretty big leap to go from robots.txt is advisory to ignoring it constitutes a criminal action.