Hmm. Maybe the programming isn't complete. I just checked mine, and one snipe is missing it as well. But it is also a fixed s/h price, listed in the usual place (not in the middle of the auction listing).
I think it depends on how and where in the auction listing the seller has placed the shipping cost. I suspect those whose shipping charges appear in the bottom section (as opposed to the text in the middle, describing the item) cause them to appear in the AS box.
Except that for the one I have that is missing, it is also listed in the bottom section (Shipping and payment details) and not in the middle of the auction. What's different about that one?