Either way, how would you know if they where complete or not? When it released, that's all their going to be able to do until the next game, where they likely will throw in the idea's that they didn't get to use in the first place. How are you able to judge if a game is complete or not otherwise?
You're the one bringing up the situation, so you should be asking yourself the question. However, if feel like you're completely contradicting yourself with the second sentence. Forza feels complete, but because there are cars added after release, that somehow means its not complete now? If they didn't give us any info about a DLC plan, then you wouldn't be here thinking about how a game was incomplete, you would have accepted it as a full game. DLC does not mean a game is incomplete.
Please, do tell me, what content was held back? I'm sure you have access to all their work schedule and planning to be able to make such a claim, right? How are you able to judge what has been held back in order to profit from it at a later date?
Odd thing to say since you are the one making a big deal about what was released and not being fine with it and implying that its not a complete game, because of the inclusion of DLC.