UBM TechInsights' detailed teardown of the iPhone reveals a slot housing a micro-electro-mechanical gyroscope. The device is absent from the iPad -- but there's an open slot for it.
Here's the same slice of the iPad's circuit board, showing an empty slot where the gyro was housed on the iPhone. Hence the assumption that the iPad is gyro-capable.
See main story, iPhone 4 Teardown Telegraphs Future iPad Gyro.
White PapersMore White Papers