Is that really true? I don't recall the product rolled out at the Live launch as having much of a distinguishing value proposition. Bing, on the other hand, is notably different than Google in several respects, so first-time visitors have a "take away" from the experience. If the purpose of the rollout ad blitz is to "induce trial", it's up to the quality of the match between the product and the product positioning to get people back for subsequent visits.

Marketing around release. When live launched it sounded like a PR move to bring their "online strategy" under one unified brand name. Basically no reason to look if you didn't like MSN. With the bing launch there was more of a "we are doing something different and actually trying to compete" feel to the whole thing. That actually made me curious enough to try it.

The difference is that Bing returns quality search results; Live search did not.

People tried live search a few times then left. People try Bing and then come back for more.