At the moment, this news going around about the discount deadline will probably be the last major boost for Windows 8 sales, as it will be free publicity working like a "80% off sale must end soon, order your copy today!" advert during the run up to January 31st.
While Windows 8 will continue to be sold with nearly all new computers, it's coming to the stage where there is little incentive to buy a new computer. For example, go back 10 years ago and there there were significant advantages to replacing your 3 to 5 year old PC - DVD playback, smooth full screen video, much better performance. For 5 years ago, upgrading over a 10 year old PC would give 1080p playback, smooth streaming video (e.g. Flash), multi core CPU and again a much noticeable improvement in performance as well as a quieter running computer.
However for most PCs sold recently with Windows 7, apart from a few areas such as gaming and video encoding performance, it's hard to imagine what advantage there would be purchasing a new PC other than to replace a failed PC not worth fixing. For laptops, while lighter light/compact laptops would be an incentive to upgrade, many are getting a Tablet instead and few are choosing Windows 8 tablets.
I know some people who are very reluctant to replace even their 10 year old PC. Their reasons are much the same - "Yes it might be slow, but as long as I can read my e-mail, use eBay, check Facebook, etc. it's fine." Like a washing machine, toaster, etc. most wait until it totally fails. Even then they still try getting it serviced to see if they can get any extra life out of it. :doh:
So it will be interesting to see the Windows 8 sales figures from February onwards.