Insane discounts? It’s a mix, really. Vista Home Basic and Vista Home Premium OEM are priced the same as the retail upgrade editions, meaning that your average do-it-yourself system builder isn’t going to save much with an OEM purchase provided he has an old copy of Windows laying around to validate the upgrade.
If you are thinking of picking up an OEM version, bear in mind that swapping out parts all the time will likely invalidate the license. For a PC that doesn’t have the parts removed or added often, the OEM seems like a steal. Well, if $200 is a “steal”, that is.
Source: Ars Technica