Obviously there are some really big assumptions in this calculation. The first is that five percent of the total Angry Bird hours are played by Americans at work. First, we don't know the international breakdown, nor do we know how often people play at work. But, five percent seemed like a reasonable assumption. Second, the Pew income data for smartphone ownership is not that precise, particularly on the upper ($75,000+) and lower (less than $30,000) ends.
I had to pick numbers, so I basically split Americans up into four categories: people earning $30,000, $50,000, $75,000, and $100,000, then I calculated simple hourly wages for those groups (income/52/40) and did a weighted average based on smartphone adoption in those categories. The $35 per hour number I used is comparable with the $38 that Challenger, Gray, and Christmas used for fantasy sports players. But this is certainly a rough approximation. Put it this way: I bet this estimate is right to the order of magnitude, if not in the details.
Now, if you really want to get huge numbers, try looking at Facebook or web-based casual gaming sites this way.