Well that's clearly not what the data shows.
This of course can't conclude this indicative of the entire WoW playerbase, but rather only the the WoW playerbase that are also members of MMO-C.
Though I suspect that we have the highest concentration of vanilla players:non-vanilla players than we have ever had. More and more people are able to prove that they've been here prior to 2007.
There is however a widely accepted fallacy that "new" players/"young" players are ruining the game and dictating the course of development. This of course cannot be true if 84% of the existing playerbase are self proclaimed "veterans". In fact it has been a longstanding hypothesis of mine that it is the complete opposite. The attachment to the time and effort put into our characters makes some of us more reluctant to let go and move on. Call it addiction, call it stockholm syndrome, call it whatever... things like LFR and catch up mechanics, the more casual, less year long devotion has enabled many of us veterans to stay playing as we "grew up" and life got in the way. As a 30 year old I have way more interests, money, commitments, dependents etc. than I did at 18. Despite the number of tales that sound very similar there are still a large number of obnoxious and stubborn asses that are convinced of their own failed logic. This type of evidence is without a doubt, anecdotal, circumstantial, but it's far more evidence than those that believe new or young players are ruining the game have.