If this isn't enough to convince you, nothing will be. I'm not sure how the evidence could be any more convincing.

Content from Google's result database ends up used to generate Bing's results, full stop. Proved. It may be technical error, it may be only used a little bit, it may be deliberate, it may be accidental and perfectly ethical by some people's standards, there's all kinds of ways to legitimately interpret this fact. But Google has demonstrated beyond a shadow of a doubt that input from Google is used to generate some non-zero bit of Bing's results. There is absolutely, positively no other explanation that accounts for the facts of the case.

"... we thought this practice was happening for lots and lots of different queries, not simply rare queries ..."

My comment was in reference to that.

I know. My point is that they've established beyond a shadow of a doubt that Google information is ending up in Bing's results. The default presumption is that any data could end up anywhere; the odd argument is that they have specially cased this and they only grab clickstream data when they have no other sources. One would expect that if the data is being collected it's being fed into the search algorithms and always being considered as a weight, not just sometimes.

I hate to be a bit harsh, but that argument sounds more like spin or rationalization than a logical argument. It sounds nice but it doesn't make sense if you try to actually map it back to the real world, where somebody had to type real code to produce the effect you're hypothesizing, and they weren't writing this code with this debate in mind in advance.

Of course it's always being considered, but the question is how much effect it has in practice. I guess this depends on your ontological categories, but personally I distinguish between "Bing is copying (if you want to call it that, and fair enough) certain Google results" and "Bing is a copy of Google" (which I think has been alleged or insinuated, but not shown). The difference is a matter of quantity turning into quality.

I think they probably have statistics that convince them of the latter, and they should show them, so we can see if people outside Google also find them convincing.

The problem is that the results would not be so dramatic. It would require statistical analysis to show that there was a difference. Most people's eyes would glaze over -- even though copying was occurring and genuine damage was being done (to market share, to business model, etc.), similar to a low-grade toxin in the environment.