^^ Since they should be similar courses, not only will the universities mind less (if they mind at all) if they do notice, it will be easy to make it look as though you are only writing one PS. Just say that you enjoy all areas of Maths, but feel that you'd like to pursue Statistics especially, or something like that. Also, remember that the Personal Statement for Maths is apparently a piece of information that they rarely use, if at all. When I applied to Oxford, stuff I'd put on my personal statement was used very briefly, either at the end or beginning of the interviews - hardly crucial questions. So I personally think you should feel free to apply for Maths or Maths and Stats.
Hope that helps!