Yours is the first explanation I've seen that makes any case for Microsoft not being intentionally cheating. All the responses I've seen from Microsoft are in the form "we're not copying Google we're just using user click information" which is poor since what Google showed is that they're associating click information with the search terms that were put into Google. But since those search terms are in the referrer URL it could conceivably be an innocent general algorithm weighing the words in the URL.

As for ignoring robots.txt, that may not be the case. Conceivably you could get the url A->B link, save the metadata for both, signaling them as related, and then check both URLs against robots.txt to see if you should have them in the index. Then if url A is ".../search?q=torsorophy" Google's robots.txt disallows it from being indexed and only url B gets in but the link to "torsorophy" is still there from the metadata.