One last time: imagine how uncomfortable Wario must have been in those tight overalls (if you can't, go wear overalls and try running around). What kind of guy walks around in overalls, anyway? A plumber. Is Wario a plumber? Hecks, no! Maybe it's just all the rage in the Mushroom Kingdom, and he's moved away and all. Also, I think, they made him look old... He might be old, but no one ever wants to look old... Lastly, Wario could be trying to get away from his identity of being a twisted, villainous version of Mario (darn you spin-offs) and get his own identity as a weird guy who occasionally steals handheld gaming systems and loves money and chocolate.
But I hope he has his old costume in Brawl... because of the whiny people complaining about the WarioWare get-up. When the first trailer was revealed and I hadn't played WarioWare yet, I was disappointed about it too, but I was being stupid. I love the bomb and "Hurry up!" on the back of the jacket... perfect.
And I didn't get very far in W:MoD... pretty boring, picky controls, mini games required to open chests that were either too easy or impossible... Wario would be enraptured to hear that the game has a fan. Go tell him.
Edit: Just one more bad joke about the "eating Kirby" image: Wario's chomping at the bit to be in Brawl! I can't wait, either!