The ethernal question:
Lot of people wonder why the dimension for an iPad wallpaper is 1024x1024 pixels when the iPad resolution is 1024x768pixels.
The answer is very simple:
As the iPad is thought to be used in horizontal position in every circunstances, the resolution will change between 1024x768 and 768x1024 pixels.
It will be 1024x768 pixels when the iPad is in vertical position and 768x1024 pixels when the ipad is in horizontal position.
What does it imply?
It implies that the wallpaper sides will be hidden in one or another way depending on the position of the iPad.
As you can watch on the picture, definitely 1024x1024 pixels are the standard size of an iPad wallpaper.