Web3S is somewhat 'close' to me given that I dedicated my very first technical post in this blog to that technology :-)
I remember seeing an announcement, then I remember seeing a lot of very critical remarks, then there were some Web3S vs AtomPub discussions, then some silence followed, and then it was all over for Web3S.
I can still link to it - perhaps this link is alive because there could be some customers out there depending on it. Either way, there could a lot of reasons why Microsoft chose to go with AtomPub.
The momentum behind Atom/AtomPub is second to none and it has some attractive features which appeal to different categories of developers.
Still, there's something positive I'd like to say about Web3s - despite its somewhat complicated namespace schemes and some other drawbacks which may've been attributed to it, Web3S XML instances reminded me, well, plain and simple XML.