I dunno...Tyranitar is a huge mofo and it just somehow seems unnatural to me that he'd be able to ride Hippowdon.
That said, I agree with Cartoons!'s sentiments 100% :D
Haha, yes, I was waiting for somebody to say that.
Yeah, Tyranitar and Hippowdon are actually the exact same height (although Tyranitar does weigh a considerable amount less).
Oh well, I've always seen the dex entries as averages; so we can pretend it's a really little Tyranitar and an abnormally large Hippowdon, heh.
I'll sacrifice proportions for aesthetics...(at least I think it's pretty pleasing to the eye, I could be totally wrong).
Edit: Actually, if they're counting Tyranitar's height from head to tail and not head to feet, the size might actually be correct. Although they're probably going be the latter.