My "logic" is very straightforward - I don't want to see the same images plastered over and over and over again while reading through a topic. It's distracting, cluttered, and not the experience I want anyone to have while browsing my site.
I understand why we want to "express" ourselves with more rich imagery in our posts - that's just human nature. I'd have an image in my own signature if they were enabled here, but I'm honest enough with myself to admit people aren't reading the page because they want to see an expression of my interests, my affiliations, or my personality - they just want to read my thoughts on the subject as quickly as possible and move on to the next page.
Likewise, when I'm reading a thread, I'm not usually interested in everyone's drift teams, their favorite bikini models, or their favorite GT5 Photomode images - I just want to see what they have to say about the topic at hand. If I do want to know more about someone, I'll take a closer look at their text signature or their profile.
