When they bought hotmail, it took them years to migrate off the freebsd boxes that was running it -- they had several failures, and when they finally succeeded, they needed several times as many NT boxes as the original BSD boxes.

I would guess that the supernode software was written by skype long before the acquisition (they were running their own supernodes, despite what the article claims -- although not as many, and most supernodes were users), and microsoft hasn't had the chance or the reason to port them to Windows yet.

It's not at all unheard of for companies to do this kind of thing as a stopgap. http://www.theregister.co.uk/2011/09/02/icloud_runs_on_micro...