Some folks pull down their pics (I've seen them state that here, when this subject comes up.), some change hosting sites without updating old threads (that would be a chore), some hosts suck?
I dunno. If you EVER see a "kitty" (or other excuse for a photo) where I've posted a pic, LMK and I'll dig up a proper image for you.
This is also the reason I "hoard" longrifle pics and used to have a pretty good collection. Some pics just won't stay up long and I'm always disappointed to see the images missing. I love to dig back through old threads.
SO MUCH can be learned from old threads, if one just takes the time to go looking for them.
edit: I just glanced at my data and do think that I lost my hoard of LR pics to the C: crash I experienced a little while back. DANGIT! will start over.