Popularity is not absolute!

Popularity seems to be not absolute at least in Web2.0. I think that that's the reason is different member system rather than it's relative conception. View Popurls.com or Popular Buzz Today!(daybox.net). Popular post in mixx.com is not in digg.com, and almost the whole is not same. User have a different standard about some url or article, but that is attributed to different member system. Digg.com want to have more user, and Mixx.com too. if value in web2.0 is how many have user, popularity will be different. After all, key point is where exist.