I'm really struggling to see that there would be any benefit to WotC whatsoever in padding these numbers. The number is fairly meaningless as it is, given that it isn't even an indication of DDI subscribers, but merely the subset of DDI subscribers who are also registered on the forums.
And if you do think that it would somehow be beneficial for WotC to fake that total, it would make more sense to write a script that just increases the number displayed by a random amount every day, rather than going to all the trouble of adding new DDI subscribers and then also registering them on their own forums.
But even that sounds like an awful a lot of effort to go to in order to fake a number that only a few dozen people reading this thread care about.