1) I dropped the BSD O/S a few years back (BTW - I have been in and around computers since the sixties, so, please don't think I am too much of a newbie)
2) Of the many reasons, security, functionality, but, mostly, their induced blow-ups and the time to fix them (not counting the ones I am responsible for... Heck... I tinker with it too).
3) The cost of using Microsoft would more than double the cost of the system (but, that is only a pittance if you wish to use costly software that is not necessary for kids, like all the unused stuff in the (for now, illegal) Word, for all the 'enhancement' they love to load for non-security, and all the overhead to needlessly thrash an ARM processor.)
4) Linux is not a proprietary, the last time I checked. And with Android, and a few other possibilities, you could thrash Windows silly, which even your article says it can be loaded with. (BUT WHY?!?!?)
5) The attitude that the world runs Windows, is changing... And the idea of not being able to run what is needed?? You have not been into Linux, Ubuntu or the real world, much, have you.
6) Since it comes with so much, runs so inexpensive (I avoided 'cheap'), and approaches more than the current idea of the Yuppy, GenX or whatever generation is going on now, and their 'latest toy of the minute' ideas, the slavish idea that 'ONLY REDMOND KNOWS WHAT IS NEEDED'... seems very short sighted. (And indeed, the knowledgeable youth and such, are using non-Windows in cell phones that are not windows, but are using other OSs... which, if they don't come with them, get hacked and installed.)
7) Most people don't need the power of Office type software. A simple text editor, or using Rich Text Format (both free) is what most need (Open Office also works, and is free). There are things, when you start getting fancy, like photo-editing (You don't Need $700 Photoshop. Besides the soon to be simpler to use Gimp, there are many other free photo editors, that for simple edits, are much quicker), Accounting (You DON'T need Microsoft's Excel) or any of a hundred other "You Gotta Have" Windows systems. There are proprietary packages and FOSS packages available to the whole world, at low and no cost that fully satisfy the needs of everyone, let alone the children this package is aimed at. Don't forget - most of the backbone of the internet is not running Windows!!!
8) I must say, with the statement you made about 'not running Windows'... You missed THE point. Not only don't the children NEED windows... With this they can grow up... NOT NEEDING IT... Unlike some who eat so frequently at the Microsoft invited only table, will not acknowledge. (I am not saying you are on that list... Which you know does exist, and probably know that those that are, never slam Redmond's output)