Let’s begin by pointing out something fishy. In the October sales figures released yesterday by the NPD group one can see a peculiar pattern of absence. Wii Music’s failure to show is strange enough, but Guitar Hero World Tour and, the latest in a rhythm games series which has sold billions, and MTV Games’ Rock Band 2, the sequel to the franchise which has sold 7 million units, are both nowhere to be found. What gives?

Apparently the answer lies in the way the NPD Group (which is the U.S. game industry’s leading sales record tally firm) issues its best-seller lists. These lists are based on SKUs (stock-keeping units), which are basically what they count as selfsame single products; a single title may have multiple SKUs. For example a multiplatform game’s different platform releases will each count as a separate SKU, and so will each subconfiguration, bundle, special edition, et caetera. Now, Guitar Hero World Tour holds no less than 11 configurations, and Rock Band 2 has 4. It would be not unimaginable then, that the games were just spread too thin as SKUs go to make it into the tops.

The raw October data released by the NPD allows one to add up the two games’ total sales. If one were to do so, one would find out that Guitar Hero World tour, which is available on four consoles, clearly won with a little over 534,000 units sold over the course of the month. Most units were sold for the Xb0x 360 with 191, 049 units. Trailing close behind was the Wii version with 182,845 sold units. The Playstation 3 managed to sell 96,657 and the PS2 came in last at 63,462. Total revenue generated by the game’s sales totaled $67.3 million.

Second place went to Rock Band 2, but it was by no means disgraceful. The sales were distributed pretty evenly between the two consoles it runs on. NPD indicates that total U.S. sales were as high as 238,128 units over the month of October. Of those, 119,569 went to the Xbox 360 while slightly less, 118,559, went to the PlayStation 3. Rock Band 2 grossed $26.7 million. It should be noted however that the PS3 version of the game arrived in stores on October 17, almost a month after the 360 version. Editions for the Wii and PlayStation 2 are expected for next month.

Not so kind was the fate of the third-place instrumental rhythm game, Konami’s Rock Revolution, which was also released this month. NPD figures show that the game sold less than 3,000 units in the U.S. over the entire month. The data shows 1,442 copies sold for the 360, 816 for the PS3, a devilish 666 for the DS, and 2 (two) copies for the Wii. The latter apparent embarrassment was due to the fact that the Wii version of rock Revolution only hit stores come November 11, whereas the other three versions started selling on October 15. The game made a meager total of $132,000 in sales.