Having spent a bunch of time in the market research industry, there are likely two reasons why NPD changed its reporting policy:
1) Sales were down (specifically renewals, as I imagine new business opportunities in this market are few and far between -- industry is shrinking not growing), and sales people were complaining that the non-renewals were occurring because customers could get the important stuff for free via PR/media. This is normal and happens all the time in subscription-based businesses, typically during recessions (like this one) where customers cut non-discretionary spending. If this were the reason, NPD might reverse course -- either a) when the economy turns up and there's more to be gained from teasing figures than hiding them, or b) when less freely available data does not lead to better renewals (quelling the "they're not buying because they can get it for free" sales rep argument). Neither could happen, and either could take years.
BUT, I don't think this is the reason, because *the biggest change is no more reporting of hardware data, and hardware data is already available to everybody through manufacturers' SEC filings*. Everybody gets the numbers, just delayed. Which leads me to believe the real reason is...
2) A big customer demanded it. Market research businesses tend to have highly concentrated sales, i.e. a few large customers buy a ton of licenses and can account for a disproportionate share of revenue. These businesses are usually the largest vendors who use their customer status to influence what the market researcher publishes, because the market research announcement themselves influence other people's decisions who don't necessarily subscribe to NPD data (specifically, retailers). The version of this reading would be "MS/Sony don't want people to know that Kinect/Move bombed." Everyone will find out eventually, but with a three-month delay until those companies do financial reports, giving plenty of time to message to nervous retailers.
[end of opinion]