In BBS, I was pissed that there was no reason for Ven's small size...Well, That and the fact that Jaq and Cinderella thought he was a mouse the entire time.
I think i heard somewhere that it was because he had done something wrong while he was world-traveling because he didn't know how to do it correctly, and as a result he was small. :/ i can't remember where i heard it, though.