I think others have explained this, but I'll give it a try anyway. Plug an SD card with photos on it into the iPad camera connection kit, and plug that into th

I think others have explained this, but I'll give it a try anyway. Plug an SD card with photos on it into the iPad camera connection kit, and plug that into the iPad. The Photos app opens, you tap the photos you want to import, and you're done. Your other cases are simple extensions of this example. The fact that an iPad can't do this right now with more file types or with a USB drive is not an inherent limitation of the approach.