You can read anything you want into figures if you wish, if there is either a) no concrete way they were gathered or, as here, b) no concrete correlation between what was measured (ad impressions) and what you're supposing (number of devices used at Christmas).
For example: Ad impressions for iPads would, I guess, cover *all* iPads. A lot of people already have iPads. The percentage of overall "iPad owners" opening a new one on Christmas morning as a percentage of the entire user base was, I'm guessing, much lower (as a percentage of total ownership) than other platforms. Those existing owners of iPads are probably likely have opened other toys on Christmas morning and not bothered playing on their iPads for a bit. I for one spent Christmas with family, watching TV, reading real books, and shooting my son's new Nerf gun. My iPad hardly had a look in for a couple of days. Now, if I'd had a new tablet (of any type) I guess maybe I'd have been surfing with it. But it's all 'maybes'...
The problem with the tablet market is that, practically speaking, Apple went straight to near-as-dammit 100% marketshare overnight. It only takes one other vendor to finally get a little traction of any size and... shock, horror, Apple's market share goes down. Market share means crap (unless you're being sued by Governments for being a monopoly). New Product X suddenly selling loads more than Long Established Product Y this month doesn't mean the end (yet) of Product Y if it's installed base is a) massive and b) happy. Too many variables.
(PS: I have both iOS, Android and WebOS tablet devices, so I really don't care as long as they bloody work and have the apps I want. Pity about WebOS though, it was cute and I liked it...)