Wp7 doesnt use an incompatible format, it uses a function built in to the SD card spec from year 1, its just never been used, outside of some security measures used on some music hardware.
That is unless you are talking about USB mass storage or played with the original HD2 WP7 ROMs.
The first of which isnt designed to work with WP7 for a reason the second of which was a temp solution to a problem which is now only seen with dual boot WP7 and Android devices.
Also, the original spec for WP7 doesnt hold manufactures to SD card placment, it actually suggests using flash (for another very good reason) its not designed to format the card as such its designed in a similar way to a computer, if i yank out one of your two hard disks setup in a split RAID , your computer isnt going to work.
For the vast majority of users none of this will make the blindest bit of difference, for the rest of us there is Xda developers.
as to the article, i hope you are correct and that its not too locked down, but you have to remember that WM failed largely because OEMs and Networks had too much say in what happened with the device, MS got slatted because Networks filled phones with crap and OEMs couldnt be bothered to pay for the correct drivers, of course the opersite is true of Windows Desktop so its a going to be a tough call....