The picture says it all. Overall, the iPad 1st generation is the heaviest with 721gram, followed by iPad 3rd generation at 650gram, and the lightest at 606grams for iPad 2nd Generation. Just for my own curiosity to compare the weight comparison for the iPads using cooking scale just to be more precise.
The iPad that are tested are all 3G except the 3rd Generation iPad.
Spec for iPad 1 on Apple website http://support.apple.com/kb/SP580?viewlocale=en_US&locale=en_US
Spec for iPad 2 on Apple website: http://www.apple.com/ipad/ipad-2/specs.html
Spec for iPad 3 on Apple website: http://www.apple.com/ipad/specs/
This is just so you get the idea. Even though the iPad 3 isn’t a 4G model, you get the idea that it is heavier than iPad 2. Everything else is the same in terms of design. The White on the iPad 3rd Generation is creamier than iPad 2 White model. I wonder if the Black is different as well.