Another interesting thing about the Wondermega is that it has a MIDI-out jack on the back. What exactly it's for, I don't recall, but I remember someone was messing with the MIDI functionality on the Sonic Retro forums a while back.
Edit: Got ninja'd by Rivet. Disregard my post.
Most of these pictures you shared are concept and provisional artworks.
The latter are used as placeholders (before the final box art is finished and finalized) in magazines and promotional material, it's like how screenshots from game protoypes end up in said places as well.