You are being short sited on the gambling aspect. It's not US gambling they are working with... In just about every other country outside the USA online gambling is legal. Europe / Asia is the market, not the USA. Heck... even Canada has online gaming and has had it for many, many years.
I believe online gambling already exists in Great Britain, and I'm sure there are other countries, so there would be strong competitive forces at work. What would make ZNGA special among the crowd? The only edge would be better odds, and hence diminished returns. The regulatory complexities still remain huge, as each nation would demand its cut of the winnings. You would need ten floors of accountants, lawyers versed in the different languages, and lobbyists with cash in hand. How would any nation enforce bookkeeping honesty on a company like ZNGA, as the whole thing is easily open to corruption?