Re: teaching computing to kiddies.
^ This. What @Richard said.
Back in the 90s, Apple was marginalised (and boy, were they marginalised!), Atari ST was dead, Amiga was dying and Linux users all had beards and eschewed soap. In the minds of the general public, Microsoft was computers - and a computer without 'Microsoft' was unthinkable.
The world has changed a little since then. It's a UNIX* world, in all its different flavours. Add up the installed base of iOS, Mac OS X, Linux and Android and its Windows that is looking a bit marginalised now.**
Raspberry Pi is part of this trend, although it's installed base is a drop in the ocean (even at 8 million) compared with all the other UNIX systems out there. Windows IoT isn't going to help Microsoft reverse the tide either - if anything, it might push more users into the welcoming arms of Linux. A noob might buy a Pi for a dabble (it happens - it's so cheap that why not?) on the strength of Windows. On discovering that it doesn't really have Windows they might give Raspbian a bash - and discover that it's familiar enough that they don't need Windows anyway. Certainly, that was Mrs. 45RPMs experience.
If Microsoft really wants to join in with the Pi fun then surely the way to go is with Windows RT and a lightweight version of Visual Studio on the Pi. With that, who knows? They might even tempt some users back from Linux***
*I know that Linux isn't UNIX. But it's so UNIXalike that the distinction is irrelevant.
**fanboys, don't blow a sphincter - this isn't a comment on the merits of a particular OS - just a reflection on the current state of play in terms of installed base.
***Probably not many though.