iPad 4 vs iPad 3: spot the differences
 

That Apple no longer makes the iPad that was introduced in March and replaced it with the iPad 4 Retina has everything to do with the Lightning connector. It now has the same connector as the iPhone and iPod, which is handy if you buy a dock for example. Apple doesn't seem bothered by the fact it has made all old docks obsolete by changing the connector, something that can cost consumers a lot of money.

http://uk.hardware.info/reviews/3585...he-differences