It seems this was announced in December.
Given the lack of discussion here I guess it wasn't in wide use. I know some who like the quality and feature set of its H.264 encoder. I wonder if the free version will live on for some time as it's a common free method to encode WMVs on Windows.
Going forward, Microsoft is continuing to invest in encoding, format conversion, and live on-demand streaming as a part of Windows Azure Media Services.
Expression Encoder 4 Pro will continue to be available for sale through the calendar year 2013. It will be supported for the remainder of its support lifecycle and no new versions will be developed.
Additionally, the free version of Expression Encoder will continue to be available for download.