I'm experiencing the same issue with output images getting resized that PPG and slash5150 reported. Any advice on this? I'm trying to figure out how my images differ from the provided sample images, but nothing is jumping out at me.
edit: Actually, now that I'm digging deeper into the PNG file info, it looks like Photoshop is throwing in some extra data if I open the sample image and then resave it.
Using ImageMagick to analyze the files, your original image shows "Units: undefined", but after resaving in Photoshop I get "Units: PixelsPerCentimeter \ Resolution: 28.35x28.35 \ Print size: 45.1499x25.3968". Both show "Geometry: 1280x720+0+0". There are a few other minor differences, but none of them seem relevant.
edit #2: Nevermind, if I create an entirely new image and set the DPI to 96, it works. Photoshop for some reason was defaulting to 72 DPI when I was resaving the included files (I assume because it isn't specified in the PNG file itself).