Stephen, thanks for the info, I hope to meet you someday soon as I plan on making at least one LSR ride in early 2014, but school is destroying me at the moment.
It's easier to forego fenders in this climate because it so rarely rains. And if it is, it's usually predictable enough to prep your bike accordingly. The main reason I'm building up my bike is for the purpose of all-weather commuting and touring. The fact that it will make a great rando bike is just a happy by-product. After one ride in the wet with full fenders, I don't see any reason to not include them on any long distance bike. I've used those half fenders on my Bianchi and they work about half as well.
As for the cost of the bike, judging by your photos, even if I paid full retail, I'd be surprised if my full build will cost half as much as some of the bikes there even after fenders and lights. But we're still talking roughly 2 grand. Again, I understand you could do this on a 100 dollar bike with 50 dollar lights, but who the hell would want to? If I'm putting in serious miles, I expect to put together a serious machine accordingly.
I had planned on a frame bag similar to what I saw in most of your photos. Definitely not a handlebar bag fan. Not like I'm fast enough for it to make a real difference.
Anyhow, getting back to the original content of the thread, I simply hoped to offer an outside perspective in the frame of the "mainstream" cycling community. Any discussion on equipment and cost aside, it's just too weird for your average serious cyclist. I think that's the main reason you see older folks getting into it as well. These people have gotten over themselves and don't mind fredding out. When you're young, it's all about the local crit and being faster than the next guy. But from what I can tell, randonneuring certainly isn't "dying" or anything like that. I think cycling as a whole has grown and will continue to. And returning to age, while cycling as a sport has grown in the U.S., the average rider age has also gone up. I've seen people refer to it as "the new golf." And on the young side, I repeatedly see articles referencing fewer teens getting driver's licenses. I imagine some of them are turning to bikes.
I think the demographic question is just too limited of a look.