That may be true, but give the guy a little credit, he created a service that has 750 million active users. How many other people can say that?
There's tonnes of sites that serve 750 million. No service that has the same amount of activity, but in 10 years a few status updates will seem like usernet does today.
People do and will remember Jackson because of the music with lasting value he left behind, not because they remember listening to that music 20 years ago.
Facebook will, wenn G+ eats its lunch in a year or two, leave nothing tangible, audible or visible behind. Facebook will be just a memory, and memories quickly fade. Do you remember browsing geocities or tripod sites? Exactly. Me neither.