Sales and ad impressions are not always closely related, especially when you consider the likely primary uses of the devices. PB, Android tab and iPad owners probably do a lot of browsing, generating more ad impressions and probably more representative of the relative number of units out there. While Kindle users are likely doing more reading and consuming of media content from Amazon, which would result in relatively fewer ad hits per user. Just a wild-a$$ guess.
I think you are right. Plenty of Kindle Fire users will consume media and never web browse, but it is the rare Playbook, Android, or iPad user that will seldom web browse.
This seems to verify that there is not a tablet market. When considering the graph with the iPad, there just isn't a second place. It is statistically irrelevant.
As for ad impressions, might the PB be aided by Flash? After all, so much of what Flash does is serve ads. Just a thought
