That is because Windows, OS X, Android and Linux allow their users to install third party programs without whitelisting them. There is nothing stopping users from installing malware. OS X and Linux have less malware because they're not as popular as Windows and Android.
That's opposite to iOS, Windows Phone/RT, XBox and Playstation which are pretty much free from malware because everything has to go through an app store.
That is because Windows, OS X, Android and Linux allow their users to install third party programs without whitelisting them.
<Devil's advocate>Then clearly Microsoft aren't doing enough to look after their own back yards, and their domains should be seized and potential Microsoft customers rerouted to information about the dangers of using Microsoft products and safer alternatives.</Devil's advocate>
This is a highly impractical response to the problem of malware, of course, but I don't find the analogy stretched at all. The action Microsoft have reportedly taken -- and the support they appear to have been given by the courts -- are just about as absurd as my tongue-in-cheek response above.
We seem to have grown up and stopped assuming everyone using P2P protocols obviously wants to pirate films, and we don't assume everyone using Windows XP obviously wants to be part of a botnet, so why would we assume everyone using Dynamic DNS obviously wants to distribute malware?
[Edit: There are now quite a few HN posters in multiple discussions about this action who are saying their innocent use of No-IP is being undermined because Microsoft's sinkhole is getting in the way.]
(unless we're talking things installed through homebrew, pip, gems and whatnot, but those aren't likely to be used by inexperienced users)
Microsoft failed to secure Windows XP against malware and botnets, so all Windows XP users will now be redirected to Ubuntu.com when they try to access the internet through Internet Explorer.