I always chuckle at these threads. Every time WotC releases some marketing numbers, we get suspicious folk questioning their motives and methods. As if the idea that "lapsed" players might include those not playing 4e is some sort of veiled insult.
WotC wants you to be playing 4e. Duh. Failing that, WotC wants you playing some form of D&D, either an earlier edition or some sort of clone, as getting your paying business back is easier if you are an active player of some sort. Heck, if you're not playing some version of D&D, WotC would rather you be playing any sort of RPG rather than moving away from the hobby entirely.
The accuracy and source of WotC's numbers are unimportant (to us). WotC's a relatively big company, big enough to be able to do excellent market research. Something they've been doing since the day they purchased TSR (in regards to D&D).
The point of the numbers is that while a lot of people are playing D&D 4e, there is a huge order of magnitude more of D&D fans and former players who are not playing 4e . . . and WotC wants to recapture some of that business. Not as an insult or to demean players of retroclones or Pathfinder, simply to grow their business. Which is neither sinister, suspect, or foolish. Quite smart, actually.