It looks like MS wants to make some more cash. The Developer Edition of SQL Server 2008 R2 and 2012 are NOT free anymore. Now you must buy it for U$ 50 or 60. Not too much, but not exactly cheap. For something you will use to train and experiment with – and then use this knowledge to convince your manager/company to buy the full version, it should definetly be free.
We still have the 180-day Enterprise Edition trial though (but I do not know if the “ManagementStudio: Complete” installed from trial will expire after 6 months or not). I also could not confirm WHEN they started this, but I guess it doesn’t matter now.
Some MSDN threads with more info: