(ms)news.microsoft.com are DNS names for Microsoft's NNTP (newsgroups)
server while Microsoft Communities is a general name for all things (one of
which are newsgroups) Microsoft has for us to interact with Microsoft
employees and uhm... community.
i think he means within the new windows mail interface... when you setup a
news group you are asked if you want to activate communities. this is the
same as the newsgroup but lets you rate posts
In Windows Mail if you look you will see that Microsoft Communities also
uses msnews.microsoft.com as its news server. However, if you use the
pre-installed Microsoft Communities it also includes the metadata to provide
features from the Web interface, like the ability to rate posts if you have
signed in with your Passport/Windows Live ID. If you set up a new news
account for msnews.microsoft.com you will not have access to or send this
metadata. You will also find loading a newsgroup to be faster.