That's probably just because Bertie is more... well, 'actively expressive' is the only way I can describe it. Jeeves is more into the 'standing quietly in the corner and thinking things out', while Bertie is an Action man.

Oh, Lordy... I just imagined plastic Bertie figures being sold in bulk...

"Get your Wooster here! Now with new improved Piano-Ability(tm)!"

(I read some of your George/Melchett, by the way. Very good. It's a fandom I happen to like. I mean, it's practically canon.)