You can expect sales in the D&D product line to decline similar to sales in iPhones. A new product announcement always kills / slows sales.
I hear this all the time in my 4e group -- sales were going strong until WotC inexplicably decided to pull the plug on 4e, at which time sales predictably fell, and besides, natural product cycles would imply low sales for 4e in any event, so really, there's nothing to see here.
And I just don't get it.
WotC invested tens of thousands of man-hours, and many hundreds of thousands of dollars, in a system they believed would carry D&D for a standard 8-10 year product cycle. Most of their designers staked their reputations on it. The fact that WotC pulled the plug on 4e years early, jettisoning half-completed products like the PH4 and discarding several years of design-and-development plans,
has to mean the system wasn't performing up to snuff sales-wise. And for that reason alone, the ICv2 figures wouldn't be a surprise no matter
what WotC had done about Next or what the product cycle may be for 4e.
But that isn't what I don't understand. What puzzles me is why so many people see 4e's sales performance as a referendum on whether 4e is a solid system, and think giving any credence whatsoever to underlying sales issues means admitting the game itself isn't any good. And it just doesn't mean that. Solid products underperform sales-wise all the time for reasons that have nothing whatsoever to do with product quality, and this may just be one of those times. It's also worth pointing out that numerous 4e design elements from themes to at-wills to backgrounds are being incorporated into Next, which wouldn't be happening if the system really were as bad as some 3e/Pathfinder fans claim.
So that's why I think 4e fans can and should hold their heads up high, which simultaneously acknowledging that changes are needed to make the game more attractive to people who feel something vital was lost in the 3e-to-4e transition. Because we all benefit when the game's base is broadened -- more designers are hired, more products are produced, and some fractured gaming tables can perhaps be reunited. That may not be a popular view from the extremes (on either side), but it's my two cents on the issue.