You are using a different definition of lossy from everyone else. Lossy means that information is lost in the compression process; the output is different from the input. PNG is not lossy; the exact image is reconstructed.
You are comparing how much original image can fit into a fixed size of compressed image. This is a backwards way to look at things. I guess it makes some sense if you are trading off compression quality, image size, and number of images on a fixed size memory card. Most people have fixed size images that need to compress to the minimum size without too much loss of quality.
The compression depends heavily on what the original image looks like. You can compress an enormous, single color image much better with PNG. JPEG would result in smaller input images for the fixed output size. For photos, the reverse is true. But this only holds when the quality reduction is acceptable. For some applications, the output image must be 100% the same as the input. Only lossless compression is acceptable in that case.
