If you were ever a fan of the Age of Empires series, you probably recognize Ensemble as the talent behind it. They were brought in for the development of Halo Wars, which still has a lot of development ahead of it. Microsoft has already let much of the Ensemble staff go, but the core development team will remain to finish the job.
This is not an uncommon sight. Large publishers like EA and Microsoft have run down or close numerous game studios after acquiring them. The memo detailing their reasons behind shutting Ensemble down was apparently leaked, but the gist of it was that Microsoft isn't planning on leaving the gaming market. As a somewhat humorous side note, Ensemble still has job postings listed online.