The PS4 has had such an insane, insane year.
Didn't it top all 10 NPDs this year so far? That must be a record.
It didn't, as has been indicated. But even if it had, that wouldn't be a record. Wii won every month in 2008. (And the only month it lost in 2007--barely, even with shortages--was
Halo 3's September.)
That's not the mark to beat for consecutive wins, though. PS2 outsold both Xbox and Gamecube starting when they launched in 2001, then every month for the next two years. In 2004 Xbox won 5 months. Then in 2005 PS2 was back on top every month, and it stayed on top all the way through 2006...and yes, that includes against Xbox 360 and the launches of PS3 and Wii.
If the sample is representative of the population than it's a pretty freaking good one to make inference on total sales in the market. In the case of Amazon, we don't know whether it's a good sample or not; now everyone buys online but I'm pretty sure some consumers still vastly prefer physical purchases.
Actually, we have at least indirect evidence that Amazon is not a good sample. Over at chartz some users have made an NPD prediction tool that relies on rankings from online stores, and it weights Amazon highly. This tool is bad at predicting sales. That doesn't necessarily indict Amazon as an unbiased sample--methodological details could be to blame--but it's certainly suggestive.