They seem to be operating with an attitude that if they can get as many people as possible to use their newest version of windows, that they will save money by not having to deal with such a diverse environment of versions.
Something tells me they looked at the way companies like google release their updates often, and by default. Release numbers are becoming less important, more of a tool for developers to use (which is what version numbers were invented for, before marketroids don't got a hold of them). Perhaps a light went on when they saw that chrome just quietly updated, without any fanfare about 'upgrading' to new whole numbers, large features just got included when they were ready, from whichever version they were releasing at the time.
This approach makes alot of sense ongoing, and in the long term. Developers in the past got used to having various versions of their desktop software being in the wild, and it was a part of life. Then people started going, hey with the web, I only need to be supporing one version of our codebase, which is actually pretty awesome. Google came along with chrome and decided that it made sense to have as few versions in the wild as possible. It seems Microsoft is playing catchup with this, but they still have large releases of windows, with interface changes between large versions, which causes folks like you to want to hold onto older versions. Seems they are still working on fine tuning their social engineering.