I believe the topic determines the length of the post, some posts need just 1-2 lines where as some posts need in-depth analysis. If you take note of real world communication you will discover that within 60 minutes of discussion people will be talking about so many things, they might start with weather, than move to game and end up talking about politics. Likewise in a forum, people could be talking about different things in a thread about Minecraft. I think this is natural. This is how real world communication goes. It is the moderator's job to remind people to come back to the topic, you cannot call everyone a spammer or low quality posters just because they are not the "experts."