A place for those who "Trust the Fungus"

On the DVD cover, the Thwomp Stompers are uneven. They both go up to what appear to be their owner's kneecaps. So as such, Luigi's Thwomp Stompers are actually larger than Mario's.

That's interesting. I hadn't noticed that before, though it does seem likely that there would be different sizes. I'm just not sure why they would bother to do so for the production or even just for the graphics.

In the world of Dinohattan, I'd say that Redstar is right--there probably are different sizes.

However, in terms of the DVD/theatrical poster cover, I'd say that it was an artistic decision. I'd bet that they're at the same height because it maintains the line of sight at the same level for that portion of the artwork--if that makes any sense.