Bloomberg West TV show totally agrees with you. They claim proving the lawsuit will be almost impossible as there are many similarities as well as distinct differences. They showed a video comparing the games while they all laughed.
In my opinion this lawsuit may even end up helping Zynga. Because, once this case gets thrown out as completely ridiculous it will give legal support that Zynga's games are perfectly fine and acceptable (assuming it gets thrown out but if you watch the Bloomberg West video they pretty much say this lawsuit is ridiculous).