"If you pay for GSX, it's not shipped, it's downloadable."
Because this is NOT what's happening! You are still assuming the product will be downloaded *after* paying ( the "If you pay" usage in your sentence ), but it's NOT!
Since we say the
download is always available BEFORE purchase, and we say you can
activate the product AFTER purchase, it's implied that nothing is ever shipped, since you don't get anything (not even the download itself) "after you pay".
The ONLY thing you get "after you pay", is a purchase receipt which contains your Serial Number that can be used to activate the product you usually have ALREADY installed in Trial mode, because this is what the site is telling you to do:
GSX is a Try-Before-Buy product. You will freely download a Demo version