I am assuming you are showing height x width, since the first number is greater than the second.
First, the ratio for the two Default images is different. And I believe that the iPad will use the explicit Default-Portrait.png over the Default.png when it is available.
The Default.png size looks like for a iPhone/iPod Touch low resolution.
If you want to be using the higher resolution image for iPad 3, the size is 2048 x 1536.
iPad 2 uses a resolution of 1024 x 768, which is fine.
Making image files sized for high res iPad 3 means that you will take up much more on the device and the app download and startup will take longer. For most games, you do not need that kind of resolution.
If you are targeting the iPhone (iPod Touch), the high resolution is 960 x 640. That is what I am working with. It sizes fine on an iPad, with discrete black bars above and below.
If your Default files are in fact in landscape orientation, with the width bigger than the height, than that explains your initial problem.
Before I was able to get the app to always go straight to the landscape mode, and the device was in portrait orientation, it squished the game so that it all fit. And looked funny.
When I meant that your Default(-Portrait).png files should be the rotated version of the Default-Landscape.png file, I meant that you should use some app to load the landscape one and flip it 90 degrees and save it as the Default(-Portrait).png files. The iPad/iPod will not automatically change orientation to best fit the image, it will shrink the image instead.
AGK Community Tester