It could just be that Stegasaurus needed heat exchangers and all those others didn't
OK. Stegosaurus stenops does have very broad, large plates with a lot
of surface area that could have worked well as heat exchangers.
However, S. ungulatis has much narrower and smaller plates that wouldn't
have worked nearly as well. Huayangosaurus, another setgosaur, had very
thin, pointed plates, that resembled spikes more than solar panels. And
finally, Dacentrurus, another stegosaur, had no plates at all-- just
spikes all the way up his back.
Caleb
http://www.geocities.com/Area51/Vault/6619/index.html