Kind of irrelevant as you're not supposed to reinstall widnows evcery 6 months or even every 12 or anything like that.
OEM versions come pre packaged with the latest updates rolled in when you start up your new computer. retail disks also tend to be semi regularly updated, but they're going away from full install disks now.
basically in General This only affects people/companies that have access to install disks with the latest updates rolled in anyway, either by themselves or a third party.
And yet some people only buy one when it comes out in retail. Everytime the need to reload, because of problems or whatnot, they still have to go through 1gb of upgrades.
With Linux, its updated to the latest drivers/software, in retail, every 6 months.