Whilst Zynga has as much right to ____Ville games as Bethesda does to ____Scrolls games, they... might have a point.
Like or hate their games (I say 'their' game; they just cloned Farm Town for most of their harvest-based browser games), they *do* own intellectual property rights for online social media browser-based games, and would obviously like to maintain those property rights in this particular medium. Much like Apple having fisticuffs with the Beatles for years-- Apple were only allowed to keep their name so long as they kept out of the music game-- DC comics don't have a presence in "Facebook games", so seeing an ad suddenly appear for "New Browser Game! SmallVille!" to the right of your Facebook status update window, a significant proportion of people (who don't know/don't give a shit about Superman or DC, including me) would immediately think it is a game 'by those guys who did FarmVille'. There is legitimate cause for confusion, as--surprisingly--out of 500,000,000 people on Facebook, more of them would know about FarmVille than Smallville.
Zynga totally have a case if DC wants to muscle their brand in the lucrative social-network-gaming medium, in which Zynga has significant market share and brand awareness based on _____Ville titles.
Don't let your disdain at an unscrupulous, "lesser" gaming company (in your eyes) colour the fact that if MegaConglomerateGloboHyperCorporation D.C. wants to bring 'Smallville' to Facebook, then the creators of FarmVille, CityVille, FrontierVille, YoVille, and PetVille, will most definitely have a strong intellectual property case against use of that title.
The fact that the name 'Smallville' has been around for x decades longer than 'FarmVille' means nothing; there has been no game on a social media platform called Smallville, ergo it doesn't have automatic trademark rights over the term in that specific medium.