I could understand this post if Zuckerberg had like a 2200 rating, or if he did an SRM last month at 4 in the morning, but what on Earth are we supposed to take away from this?
I rather suspect cultural memory is short-term.
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.
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.