I dont know why it allows a method in an asp.net form because any asp.net form (i.e. with runat=server) will always post to itself.
I highly recommend you consider using this model because it works quite well and in most cases posting from one form to another can be avoided.
If however you really need to do so there are ways to do it without posting the form to another page using cookies or session variables and then redirecting to your second page.