What you are describing is called the cyber neural accustomation phenomenon. Basically our collective unconscious becomes more comfortable when there are more individuals and the site is around long enough to seem reliable. The opinions become more complex as people start to rely on the medium more hence making longer posts and responses. Also with increasing 'familiarity' with others people they tend to express their opinions with less fear of a outcasting backlash to their comments. I'm just making shit up.
You are good at that. Most people think ending a post with "yo, ho to Bel-Air" is good enough. Had me until 'opinions become more complex'. Really, I didn't believe it at first -- but the Internet made us dumber. A lot dumber. I think we're finally starting to rebound.
I think you may be on to something- namely the making shit up part- though your hypothesis may hold water- especially if it takes the form of a galvanized portable bath tub. Actually the tendency to retain a longer attention span and thought process necessary to make longer posts could be a side effect of heightened geomagnetic storms resulting from increased solar activity creating a shielding effect over the surface of the globe that reflects thoughts back into our grounded consciousness instead of those thoughts radiating harmlessly into space. That way our attention to what we are writing is enhanced and we are tending to express ourselves more fully while wearing big floppy clown shoes.