I noticed this as well. In an extreme case, we may see very small variance among placebo or control groups and several clusters in the group using an experiment

I noticed this as well. In an extreme case, we may see very small variance among placebo or control groups and several clusters in the group using an experimental drug. If one or more of those clusters significantly beats the control group and we can accurately classify patients into clusters, that's important information which simple means and medians may obscure. This reminds me of the importance of looking at data and Anscombe's quartet [0]. [0] http://en.wikipedia.org/wiki/Anscombe%27s_quartet http://en.wikipedia.org/wiki/Anscombe%27s_quartet