It is possible that they overpaid based on the success of Draw Something, but they could release another star app with the Omgpop team, or even improve their existing apps! I guess we'll find out later...
The cost of building that game are also the lessons they learned along the way. Also, for a team of developers, server administrators, project managers, I'd imagine their salaries for their services alone not including office space , computers and services would've cost way more than that.
I think this is a great article. OMGPOP didn't have the advantage of hindsight in building their product. I really doubt they knew what they were doing. Their advantage was being agile and adjusting their game and business model to how the crowd was playing the game.