This is actually a good question. Posting pictures of your system should be promoted, especially if you hold yourself out as an expert and perform reviews. The value is not in seeing the equipment, but seeing the listening room and how it is setup.
Few things impact the sound of a system more than the listening room. I know if I move my listening position or speakers 12 inches one way or another, I will change the sound probably more than an equipment upgrade - not to mention the effects of furniture/room treatments/etc.
Just take a Radio Shack SPL meter and measure your inroom results compared to the equipment specs. I doubt anyone's room remains +- 3db throughout the entire frequency range (even with a dedicated listening room and extensive treatments, I'm lucky to stay that close in just the majority of the primary listening range. Without proper setup/treatment, it was much worse). In short, room setup can be just as important as the components used.
Now, can you tell very much from a picture? No, but I'll give you an example where it helps...
I don't want to name the particular audiogon member, but he very often posts strong opinions on the merits of the gear he uses. When you look at his list of equipment, it is very impressive (probably close to $20k). However, when you look at the pictures of his setup, it almost totally sabotages my confidence in his reviews. It's not that I doubt what he's hearing, but when you have a cramped room, speakers squished together, a big screen TV almost touching them, no window treatments, etc, I'm very confident saying that he is not getting near the best out of his equipment and thus one should properly weight his comments on comparisons of equipment made in that room.
In fact, I've always wished the professional reviewers would publish pictures of their listening rooms in addition to the equipment being reviewed. I don't claim to know it all, but I'm also not going to blindly follow a reviewers advice without feeling confident in their abilities. Adding pictures of their systems is one way a reviewer can help gain credibility with discerning readers.