You might not agree with the reasoning, but MS is doing this for business reasons. It has realised for many years that it can't go on just doing more of the same thing, with evolutionary tweaks every few years. By 2020, things will be very different from now, and doing the same means signing your own death warrant.
What we are seeing is the start of a radical transition. It's very risky indeed, and MS knows very well that its entire future is at stake.
* Most corporates have just moved to Win7, and will skip Win8 anyway, even if Win8 was a super-Win7. Those that don't will use the Win8 downgrade licence to install Win7.
* Win8 is primarily about the Consumer space - people who barely understand the issues we talk about every day.
* Outside of corporates, 98% of Win licences are on new PCs, and they will be Win8. Of course they know some retro geeks will downgrade to Win7, but not nearly on the scale of Vista-to-XP.
* MS must address the devices market (tablets, smartphones, etc) space before it's shut out permanently by Apple (Android just isn't cutting it in tablets; Nexus 7 is mainly to stab at Kindle Fire). The opportunity in the devices space is considerably larger than the desktop space. The next two years will be decisive. iPad-style users will like WinRT devices (ARM), and businesses will go for Intel version.
MS is going through a profound, radical change.
* The Office licensing model is transitioning from licensing a device to licensing a person. With the next Office consumers get 5 licences, and you decide where you want to install - and that will include IOS and Android versions. With WinRT and OfficeRT, version numbers and year models disappear ... you always get the latest version with your subscription. You also get 365 minutes of Skype credit (ie calling paid phones; normal free Skype continues).
* Servers, Exchange, SQL and other key platforms are changing deeply.
* Online/Cloud integration with local/device systems is coming together in a way that radically changes the whole game.