Besides, does it really count as "mecha" when the legs are just sticks on top of wheels?
I still consider the exposed pilot a sticking point, the crew of a combat vehicle belongs into the most heavily armored part because a crew kill is the worst way for a vehicle to be lost in combat. Stick some proper plates on there and use a viewing slit or a camera like a sane designer would FFS. I guess they know they don't have to worry about that in paintball (unless someone adds a "pilot hit = instakill" rule) and are thus cheating a bit with their design.
Also it seems to me that the US one was specifically built for paintball whereas the Japanese one is just something they built in general (if they haven't even accepted the challenge yet have they even built paintball guns for it?). That "LOHAS Launcher" thing doesn't look like it's meant for paintball, for example.
Hm, would it be a good idea to have some sort of televised tank competition where people have to build actual tanks and shoot each other with them (only remote controlled vehicles of course, maybe with a dummy crew)? If nothing else DARPA could make a competition like that.
I swear that thing is playable in Chou Soujuu Mecha MG.