of course it's true. it's even true with the iPad Mini. it ships with the same 5W charger that comes with the iPhone. the charger gets extremely hot to the touch when charging the Mini.
just for shhh*ts and giggles, i tried to charge my iPad 3 Retina...and it could barely be touched.
if you think i am making this up, search the forums for the 5W charger overheating