There is a possibility that the order (bottom up, or top down), is a function of the browser that you are using. There's nothing in the HTML form specification that state that the input fields must be sent in any particular order. I remember having to deal with these problems in the early days of HTML3, when some browsers would return the form elements in the reverse of the order that they were presented on the screen. (I can't remember which one it was, however... as there was only really lynx/mosaic/ie/netscape at that point, you'd think I'd be able to remember)

For the most part, browsers do send their information in the order in which it was in the HTML document (which may not be the order it was displayed on the screen), but it's possible that others may send them in tab order, or whatever else they believe makes sense, or is easy for them to deal with, as there is no specific requirement on order.