Buy & Hold may still work
Personally I downloaded the Win 8 "Consumer Preview" which came as an ISO file and installed it to a VMware Virtual machine. The Win 8 Release Preview acted the way you describe in that it downloaded a 5 or so MB installer. Assuming you're correct and that is how this $40 licence upgrade will also work. It still may be possible to get it and hold it as, if the upgrade works "exactly" like the Win8 Beta RP upgrade, there was an option within the Installation to download and create an ISO file to install on another machine or partition, before it installed over your current OS. So it might be possible that you could create an ISO to upgrade from later (naturally by burning it to a DVD if you are upgrading on a physical machine). But that assumes they do it "exactly" like the Win 8 Beta upgrade. MS may take that option out, which would be bad IMHO, As the only reason I would consider this $40 upgrade is if I could use it after a service pack is released, also knowing that if I waited that long it would likely cost well over $100. I guess we'll just have to wait and see how the download is actually offered & if it has some kind of special terms & conditions to it.
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