I always thought it was a bit "lazy" doing it that way to be honest.
I kind of prefer "catering" my uploads to wherever I'm logged in, so a shot which might go on my portfolio will be different to whats on my Facebook or blog. I guess its because people will follow me in various places so I don't want them to get bored by seeing the same thing uploaded/notified in various places. Its a dream for the websites though who offer that "function" - free advertising in the way of spamming friends lists. Kind of like the annoying folks who spam you with game requests, I see the "entry to whatever competition/ new image uploaded/ just posted a share a shoot thread" type posts in a similar way.