"Can be seated", is the operative phrase. No court, no where can "unseat" a sitting member of the House or Senate, even if that member obtained the seat through fraudulent or otherwise criminal means. If the member has not yet been seated, then that's another matter altogether. But, in Obama's case, he was Inaugurated. A court can't "undo" an Inauguration. It's as simple as that.
If Obama failed to qualify in accordance with the US Constitution it's a simple as that.