It is flawed, no question. Here's the thing... with digital, particularly digital sales, units can shift dramatically based on discounting. A STEAM or PSN/XBX sale of a game at 90% off can shift tens or even hundreds of thousands of units. A game may sell more units in one day at a significant sale price than it did life to date up to that sale.
So, had we kept the ranking at units, it would be incredibly easy for someone to manipulate those rankings.
By using revenues, we are able to normalize the units with pricing. Again, not perfect, but better than units alone.
We have most of the major publishers participating, but not having Bethesda or Battle.net sales hurts, sure.
The truth of it is that without all publishers participating by contributing digital data the way in which it's being presented is inherently misleading and not actually informative as to the health of the industry as a whole. What it really comes down to is that despite NPD receiving more information than ever from participating parties the way in which said information is presented to the public (digital revenue charts w/o any platform ranking info on a per title basis) comes across as obfuscation. The public simply isn't getting nearly as much reliable information for analysis.
This could be solved so easily by providing additional rankings based on unit sales at retail only with platform ranking in addition to the current digital revenue information. Doing so would be giving us additional information to discuss on top of what we already had for so many years. But instead NPD has opted to provide us with less instead of more despite reveibvibg that additional information.
At the end of the day no matter how you look at it the information we are currently given is not only not painting an accurate picture of things due to lack of important data but also provides us with less data for analysis than ever before and it's incredibly frustrating for those of us interested in discussing and analyzing the health of the industry as a whole.
All the digital rankings are for full game spending only. DLC/MTX is not included. Hopefully we get there someday soon.
Personally I would be far more interested in a retail unit sales chart with an accompanying total digital revenue chart that includes all digital revenue and not just full game purchases as I feel that would provide a more comprehensive look at the industry and where it's heading. This is an especially interesting topic due to the prevalence of in game transactions and post release content in today's software landscape. It would be incredibly interesting to see how such monetization efforts are paying off for publishers on a per title basis and would help us track and analyze the industry form a completely new angle. It would simply give us a lot more to consider and discuss.