An "Attachments" field has been requested for the quick reply box a few times now, but WDZ is right, the ordinary reply page would be completely redundant if it was added.
I can't decide whether that's a good thing or a bad thing though. I suppose it would save a little bandwidth if nobody needed to use the ordinary reply page anymore, but I also suppose that the saving would be minimal and hardly noticed, making such a change a little...pointless.
Personally, I don't see any reason to change things.
/ 
