The main distinction of porn with a story genre from regular porn is the presence of a coherent narrative. Regular porn often jumps straight to the sexual action, while the story genre tries to add some kind of story framework around it. But in the end, both are adult-oriented and feature explicit sexual content.
Well, it's hard to say for sure. The concept of 'porn-like' is quite subjective. Some might consider certain novels with excessive sexual descriptions as such, but it depends on individual perspectives and cultural standards.
In many places, 18+ porn comics are considered illegal. This is because they can have a negative impact on society and violate moral and legal standards.
Well, there are indeed some GTA Online cars in the GTA V story. For example, certain high - end sports cars or unique vehicles that are popular in the online multiplayer might also make an appearance in the story. However, not all of the Online - exclusive cars will be in the story. The developers usually select a subset of vehicles that fit the narrative and the overall feel of the story mode, like those cars that might be associated with a particular mission or character in the story. This helps to bridge the gap between the two modes to some extent.