In my opinion, they are all different communities for different types of people who like to discuss different types of topics with a different style of posting. You're right on the ball when it comes to what they are for but in the end, when you decide to just go there you either fit in with the community or would have a hard time for a while until you adjust to fit that community. This isn't just spam that does this but is in fact all of them. 

If you like to just chill and write short posts and joke with little ability to debate, or if you're the type of person that is too hardheaded to think about and accept other points of view or tend to ignore facts, OT would probably look at you like you're retarded and would probably tear your shit up. Same with spam but instead you also shouldn't take things as seriously and view 90% of everything as a joke. 

I never been in member lounge so I don't know much on them but I'm pretty sure that there is a type of person that they don't accept... They seem like an always happy and friendly bunch so they probably don't like people who are naturally ass holes or mean (unlike spam where they are worshiped as long as they are witty while doing it)

This is just my observation... Overall they share a few similarities though in the end it's all about the community. I know most of the spammers who post, I'm sure OT members know most of the other OT members and I'm sure the same goes for ML. (maybe not since they have/had such a large number of members)...