I think the method behind s2png is converting binary data to RGB(A) pixel data, so the result should be a perfectly valid (albeit weird-looking) image. As a bonus, you automatically gain Zlib compression of your data through this method.

No, what you get in the end is valid PNG files. Here's one you can examine for yourself: http://pathg.com/i/1wI2a8kMG6.png. (Within it is an ISO of the QNX network demo disk from http://qnx.puslapiai.lt/qnxdemo/qnx_demo_405_network.iso)