Why using (push-mark) ?

What's the reason for [beginning|end]-of-buffer using `(push-mark)' ? I find this very annoying in most of the cases (M-C-[<|>]) because it breaks the expected behavior when the mark is already active: if you type C-SPACE at the beginning of a line, and move around with the arrows, C-n, C-p or whatever. The mark stays at the same position, which is good IMO. Now if you use C-> or C-< this fucks up your previous mark. I'd like this behavior to go away unless there's a very good reason (that I missed) to have it. --didier