If I had to guess, I'd say in the early days of development the iPad had a camera, but later on they realised it didn't fit in with the ideology of the device,

If I had to guess, I'd say in the early days of development the iPad had a camera, but later on they realised it didn't fit in with the ideology of the device, scrapped it, but didn't bother creating a new mould for something a user would never see.