As you can see above Portal 2 has received 3 updates in a small timespan. No new additions have been added however they include MAJOR fixes to the game finishing issues that have plagued the game SINCE THE START. There were additions to controller support and in the Feb 19 update, they added a 360 spin option to the game.
If you are unaware the 10th Birthday of Portal 2 is coming up on April 18th
Perhaps they have something planned?