I would say say that that your perception is off with regard to market share if you're talking about new style apps using the Windows 8.1 SDK -- Windows 8.0/8.1 combined account for only 11% of OS market share according to the Steam hardware survey. Windows 10 currently accounts for 46% (with only 3% of those 32bit) and Windows 7 accounts for 36% (with 20% being 32bit). In other words, you don't gain much by addressable market by setting Windows 8 as your minimum bar -- it seems to me that if you're going to go through the trouble, you'd want to go back to Windows 7, not 8 -- and by not fully embracing Windows 10 UWP over Windows 8, it costs you being able to reach XBox (assuming you were accepted into ID@XBox) which is one hardware configuration with a 20+ million install base.
That said, those are the July survey numbers and the Windows free upgrade offer expired at the end of July, which probably prompted a final push for people to upgrade (anecdotally reinforced by the panic on my facebook feed). I'm really interested to see august's survey, I expect a larger than usual decline for both Windows 8 and for windows 7, and I would expect Windows 10 to reach perhaps as high as 60%.
After that, Windows 7 will remain a relevant, if ever-shrinking, market for probably another year or two. Windows 8 will be even less relevant than it already is.
