As has been mentioned before, I believe that this is part of why MS are making such a big deal of the 'Windows 10 will never be finished' message they keep repeating, as it allows them the freedom to ship knowing that there is plenty of stuff that is yet to be done, but didn't high enough priority to stop shipment.
W8 and WP 7/8 shipped with the same kind of mentality. That didn't work so well. I wish Microsoft would learn from their mistakes and put out something that is superior rather than a clusterfck of a half finished product. They compound that by totally ruining the touch experience with W10 (not learning from their mistakes of ruining the mouse+keyboard experience in W8). As a developer I love the idea of UA (or whatever they call it now) but the idea of one OS to rule them all was already tried by Ubuntu and never took off. Why do they think they can succeed where Ubuntu failed? because there are 450 million Windows 7+ PCs out there as a captive audience? (Sinofsky's excuse at Build 2011)