If they succeed, wouldn't it be essentially overturning 17 USC 102(b)? If none of the graphics, code, or names are stolen, wouldn't this fall under a method of operation?
Also see this discussion on misc.misc, circa 1990, re: the Lotus 123 spreadsheet wars:
If the plaintiff cannot show that
the target customer audience is UNlikely to recognize that the defendant's
product is not the same as the plaintiff's then recovery is barred. Mere
similarity between plaintiff's and defendant's products is not sufficient
to support a successful lawsuit.
Zynga may have a case here if they can prove that there was intent to make users think these were Zynga's games.(i am not a lawyer, i just cut-and-paste from USENET)