The key is the last line of the press release.
The accounting charges associated with Blizzard's reduction in workforce are not anticipated to be material to Activision Blizzard, Inc. and were included in the 2012 financial outlook that was provided on February 9, 2012.
I worked at 2 BigCo's while they went through layoff periods. What people don't know unless they've worked at a BigCo is that a significant number of its employees are interchangable or in some cases just dead weight. For every department of 10-20 people, there are 2 or 3 that have the bulk of the knowledge and do the majority of the work.
There is a lot of hassle with firing a single employee at a BigCo, even if that person contributes very little, is a detriment to the team, or is abusing corporate policy. There is however an upside to getting rid of a bunch of people at once, especially when it is around the time of the anual report, and it mitigates a lot of the downsides you have when firing just one person.
Except in the cases where an entire department was eliminated, I would say about 85% of the people who were let go during a large layoff were not really a surprise.