Juggernaughts came in at least two varieties... Basically the same thing, only smaller. There's actually possibly more, and possibly smaller, depending on the EU. The concept art for it had it massive, like an AT-AT, while EU's slipped them in here and there and they get increasingly smaller. Likewise the one in ROTS was smaller than the concept art (and the concept art's actually been used in EU itself).
So consider the Juggernaught kind of like the Octuparra droid... It maybe comes ina lot of different sizes, from pretty tiny all the way to friggin' huge. That EU BS is maybe enough for me to ignore the scale issues on this... I'll only be buying one of these though I'm pretty sure.