It's a hard statistic to judge by. The economy is also many times worse than when Vista was released, and paying any amount of money to upgrade to a new OS is not an option for people.
I agree that it is difficult to judge by one statistic. Still, the trend isn't reassuring (at this point). Overall though, consumer electronics did very well during the holiday season, certainly when compared to 2011. How much that bleeds over to new OSs is conjecture.
"MasterCard—which bases its estimates on aggregate U.S. online retail sales transactions among more than 60,000 merchants in the MasterCard payment card network—notes that online retail spending rose by double-digit percentage increases during the last two weeks of November, and recorded 19 days when sales “easily cleared the $1 billion mark.” It notes that the peak online spending day of the season was Nov. 27, the Tuesday after Thanksgiving, with close to $1.5 billion in online sales, and that several peak spending days occurred between Dec. 10 and 14, when consumers spent an estimated $6.9 billion online. MasterCard adds that specialty apparel and consumer electronics showed particularly strong online sales during the 2012 holiday season, with each category doing more than 20% of their total sales online.... Store sales, by comparison, were weak, according to the International Council of Shopping Centers and Goldman Sachs Weekly Chain Store Sales Index, which reported today that it estimates combined November and December 2012 store sales to rise 3.0% over the same period of 2011." - https://www.internetretailer.com/2012/12/26/mixed-messages-holiday-sales
It isn't easy to measure the economy...
"Consumer spending accounts for roughly 70 percent of US economic activity, making the holiday shopping season a big driver for the US economy. Traders at the stock market will likely be watching America’s spending in the coming weeks to see how strong or weak it is. The amount that people spend during the holiday season can be a strong indicator for how the country is recovering from the worst recession since the Great Depression."
Consumer spending is a rough measure and it was up significantly. While not being an economist, I think it's fair to say that the economy was certainly improving over what it was from 2008-2011. Consumer electronics spending actually dropped 5-6% in the 2011 holiday period.
Apple pulled in almost 20% of consumer electronics sales this past holiday. (http://www.theverge.com/2012/2/13/2796086/npd-apple-us-consumer-electronics-retail-sales-2011). None of this is reassuring for MS.
As I said in the OP, I couldn't find actual (first source) statistics on sales by OS.
Since MS isn't pulling W8 anytime soon, time will tell. One thing which might help MS is Dell going private. That might stabilize the PC market a bit. I can't help but wonder if W8 will overcome the momentum Apple, etc. have.