You 're right wrt earnings (zynga had $0.85B vs facebook $2B in 2010). Zynga will probably earn $1.8B this year (http://blogs.forbes.com/afontevecchia/2011/03/02/zynga-revea...). I can't edit the previous comment, though.

Still, for a company that is essentially a parasite on facebook, the money they earn is staggering. They could even earn a lot more if they used advertising on their games (they stopped using ads in 2010).