A dozen versions, sold by dozens of manufacturers. Android is so fragmented it's hard to actually consider it a single thing. It's like saying "4.5 million computers are sold every 3 days".
The iPad is one thing, made by one company, that comes in two sizes.
With different resolutions, different storage capabilities, different memorysizes and computational capacity. Some with mobile broadband, some without.
Which may be used with or without accessories such as a keyboard or stylus.
Legitimate question: Aside from the obvious culprits (Android phones, tablets, Nooks, and Kindle Fires), what other devices are considered "Android" devices?