Then again, what difference will you be able to tell between the army of 10.1" tablets with FullHD screens and that 9" 2048*1536?
Amazingly, none.
The only reason for that stupidly high resolution is the fact that Apple is afraid of even trying to implement a decent scaler.
Otherwise, 1600*1200 would have been just as great, without the fact that they now lack the huge bandwidth required for feeding that screen at its native resolution.
So yeah, it's just this one thing for all the fans to brag about the device while everything else gets easily surpassed.
It's not just scaler. You can't solve all problems with a decent scaler.
There are two issues to consider. When iPhone 4 was introduced, it has higher resolution, so if you run old, lower resolution applications, you can use a scaler to match the new resolution. So in this case you don't need exactly double resolution. A decent scaler would be fine.
However, Apple also wants developers to be able to move their applications to this higher resolution easily. Basically, all you have to do is to provide double resolution images for all your image assets. You don't need to modify your code at all. This is actually very important, because most applications, no matter how it's written, can easily take advantage of the higher resolution just by providing better resolution images (program generated images, such as text and geometries, automatically take advantage of the higher resolution).
If you provide a, say, 1.5x resolution, many program wouldn't work. Seams may appear in image tiling, which will require heavy code modifications to eliminate completely. Worse, some problems may only appear in certain scale of zooming. It will be a nightmare.
So, double resolution is not just because Apple is lazy. It's because Apple knows software developers are all lazy. And that's the universal truth.