I dont think we should connect style with ACP style. These are 2 different parts of the system. You can use not prosilver based style or you can use heavily modified prosilver based style and it will not work. If there is different name for form_name = 'postform'; it wont work in ACP but it will work in style. And yes I have seen prosilver based styles which changed this "postform" in JS and in html too. What then ?