"every other version out there" - there aren't very many IDW Sixshots out there to compare it with. Hexatron (and its Clonedroid KO) I think are the only one in a similar size? He looks really big, chunky, blocky proportioned limbs, etc. Compared with their Optimus Prime from the same line, the OP figure looks more lithe and ninja-like in that regard. And of course he's IDW - their entire line is IDW. Same reason MMC's Overlord is IDW inspired - that's their thing. MMC doesn't do G1 style or MP figures except in their Ocular Max line. GCreation doesn't do G1 at all so far. So there really wasn't a specific decision to make for this particular figure to be IDW vs another design aesthetic - it was foregone because that's what they're already doing.