Here's PS3 version,

And Xbox 360,

First, I thought it's nice they doing fan service to include bonus characters.

But now, they're on boxart, too? 

Maybe only i Jap boxart. They usually get diff boxart. No Wii version? Or is it not coming to Wii??

Hasn't the boxart for the EU/US-versions been out for ages? And they also had Star Wars-characters on them. It's not really news.

The US and EU boxart I think has been shown, and looks good
they had Hehatchi on the boxart in SC 2, so they are doing the same thing again

i'd assume the characters are a selling point to those who wouldn't normally pick up a Soul Calibur title, while the people who normally would, would already buy it

they are on the box-art, because they are selling points and the license obviously wasn't cheap aswell, but I agree, that bonus-characters should be surprises ...

If it helps selling more copies, why not?

 I don't know.  Liscense might of been cheap.  After all their is some cross promotion going on with Force Unleashed guy being in the game as well.

Probably figured that putting in more crossover characters would put it over the line of "cool option" to "whoring gimic."

I mean if you had Star Wars, Altair and/or Prince. May as well get a few more liscenes and make a Smash Bros type game.