If we make an assumption that the difference in the two groups is simply a shift in location, we can say that the test is a test of the difference in medians. However, if the groups have the same distribution, then a shift in location will move medians and means by the same amount and so the difference in medians is the same as the difference in means. Thus I think the Wilcoxon-Mann-Whitney test should also be a test for the difference in means.
It is right? How about a confidence interval for mean difference, comparing with a Hodges-Lehmann estimate.