Because it's still beta Patchou decided to not label is 4.80 yet, but it is the version you are looking for with full Live Messenger 2009 compatibility.
Once the beta has proved to be stable it will be labeled 4.80 and replace 4.70.334 on
http://www.msgpluslive.net/download/. That will be in one or two weeks. For now just be sure to not hit the giant "Download Now" button, but get the beta below it
.