I've said this before, but Mario Strikers was never a popular series in Japan so I think its unfair to judge it only from Japan. In fact it's selling fairly well in Europe. I doubt it would do crazy numbers but I think it will do pretty good long term.
Mario Strikers Charged ended up selling a few 100k in Japan, despite selling only slightly more than Battle League in it's first week.
That said, I've just checked and Mario Tennis Aces had a 42% third week drop and Mario Golf Super Rush had a 45% third week drop. So Strikers' legs aren't to bad.