> If I play correspondence chess over email, would the email host be running an online game service? If someone modifies the Battle of Wesnoth network code to run over IRC messages, would the IRC host be running an online game service? (What about decentralized network game protocols?)

It's simple, Every MMORPG or online-game requires a license. The government can fine your company for violations. If you run games through email or IRC, pray your underground game network doesn't attract attentions.

btw there are tons of "grey" area online game services in China.