There's been 100 million iPad's alone sold since they came on the market, they are absolutely everywhere, lol. That's not even counting the other makes and models, Android, Windows tablets, hell - even touchpads and playbooks, not to mention low cost ones like the Kindle Fire.
100 million iPads and more from other parties, maybe, but that doesn't mean there's that many people
using them - particularly not the iPad, with Apple's carefully-cultivated disposal culture. How many of those 100 million are actually in use, and how many were discarded when St. Jobs introduced the New Model? How many were bought by people who'd never owned a tablet before, and how many went to the True Faithful doing the Obligatory Upgrade?