The original game does come with one free month. It's a standard for all sub based MMO. But an expansion never come with a free month. It is my belief that this is wrong. An expansion should always include a free month.
if you buy an expansion pack, you can't even play the content you bought until you also buy at least 1 month playtime. I am not arguing for or against sub model, but if you spend $40 in an expansion, you should be given some time to try it.
this could even help the game gain popularity.