Not sure that this would be good or even happen. With regular skins I think it is okay.
You know what the Master Skin costs, if you also had the download numbers you would then have how much the skinner has received in revenue from that skin. You don't need that information, as a user or customer, for any reason.
I understand what you are saying, you would like some way of telling if the skin you are looking at is popular or liked by the community. Is it of a quality that you wouldn't mind paying for it. I don't know how you do that with Master Skins other than reviewing it's download page, looking at the screenshot, which you can zoom in on and reading the comments. You can also go to the skinners personal gallery and look at their collective works.
Here is something else to think about, on regular skins people will download them and may decided that the skin isn't to their liking and uninstall it. Their download though is still reflected in the total.