Not in this case, no. They were trying to replicate Microsoft's results, which entails using a similar sample size.
I think the right thing to do is to conduct a much bigger study, get a much better estimate of the preference distribution, and then derive the % probability of getting a result at least as favorable as the Bing result by pure chance.
If you can show there's only e.g. a 1% chance that the Bing result arose through random variation, then Bing definitely has some tough questions to answer. (e.g. did they run 100 different studies, and just cherry-picked the best result).
Incidentally, you don't need a giant sample to estimate the variance on the Google/Bing ratio -- you can use any number of resampling techniques like bootstrapping to get that estimate.
(Note: I work for Bing.)