TMS, I rarely disagree with you, but I must suggest the situation is slightly more nuanced than "Google doesn't use bounce rate"
Personally, I would imagine Bounce rate is a strong signal. Immensely strong. Just not as a RANKING factor.
Given that Google has already profiled the searcher (intent, habit, stage), bounce rate will help CATEGORISE the site they landed on. "Success" might be a bounce.
Once you start thinking about what Google already knows about the referal, especially what they statistically know about a set of referals, bounce rate becomes substantially less noisy. Its about predictions and variance, stuff Google goes well.
Unfortunately, from the site owner perspective, you just see "Bounce Rate". Which is meaningless.