Now that I'm a full fledge personal Apple user (at work, I'm still a Windows 7 notebook user) - phone, tablet and home desktop - I don't really follow Microsoft's Windows timeline anymore, save for the bits of news now and then. I had not known about the Windows 10 technical preview had it not for my Apple news RSS feeds.
Hence, you can forgive me for being surprised to only just read about Windows 10 being the "last Windows release".
Switching to the Windows-as-a-service model is a significant change to Microsoft's business model, even more so because Windows 10 will be a free upgrade to anyone running Windows 7 or later. Traditionally, Microsoft has charged a nominal upgrade fee for existing Windows users, but now the model appears to be, "You buy once, you're in forever."
That is, as long as your hardware (or whatever Microsoft want you to believe) still supports the latest update, much like Mac OS X, iOS and Android.