1) I actually play Classic, and I see the amount of people first hand and how many people from the friendlist are gone or not.
2) Player activity from sites that use add-ons. It's a very, very rough approximation, but it is still statistically relevant. New expansion peak in WoW usually see a drop-off of about 50 % in one or two month. It took several months for Classic to reach the same level (notice it's about
activity, not
subscriptions). Of course you always need to ignore the current month, which can show huge spike or collapse depending on the cases, due to how the data is harvested.
Whose are "those" ? The haters from MMO-Champ where half of the posters in the Classic forums actually loathe Classic and have been trolling for years before even the release ? I certainly don't see anything of that in-game, where OVERpopulation has been the main complain up to december, and 90 % of the complaints on the Blizzard forums are about PvP.
Certainly not "greater than Blizzard anticipated" considering Blizzard "anticipated" FIVE TIMES LESS servers than we have now, and yet most of them are still "high/full".
But I guess taking five seconds to check is still beyond the intelligence level of the average hater on MMOC
Sure mate !