As Mr Heathcote pointed out, the graph itself is a bit silly, but the idea that the basic unit of digital communication is "the website" has certainly peaked. (The meaning of "website" in this instance is hard to define, but we know it when we see it. And it probably involves a single URL that everything is hung from, an "about" page, legal disclaimers, some pointless Flash and a rotating product shot.)
Heathcote uses some Soho restaurants and cafes to illustrate his point. These places would once have had their own website with menus, opening hours etc. Now they just have Facebook pages and Twitter accounts. No-one has to remember the URL, they just remember who to friend and who to follow. Keeping these things up-to-date is easy when that's the prime purpose of the tool you're using. No need to wrestle with proprietary web software, you can update your promotions and special offers via SMS.
So while these things technically sit on the web, they're not from the static web of sites we used to know - they're from an emerging web of data and relationships that gets constructed on the fly.
All of which makes it harder again for the old-school branding artists who had just about bent the web to their will by inventing the brand microsite: a tiny perfect world where the experience was perfectly in line with the mis- sion statement and the image attributes. A virtual world where the logo was a game, everything was on-brand and no pesky customers would poke their heads in to mess everything up.
Unfortunately, none of that's any use to you Post Web. Facebook and Twitter are the channel and the experience; you get a tiny icon and 140 text characters to deliver your brand values - echoing the tone and manner of the TV ads isn't going to get you anywhere. You have to optimise for interesting and usefulness, not for brand character and consistency. So if you can do interesting and be on-brand and squeeze it through a social service such as Twitter, then you're really on to something.
That's why I love the Kleenex Hayfever Mashup (Google it, or maybe even Bing it). It uses Twitter, a map and the gripes of Twittering hayfever sufferers to create something interesting, on-brand and even slightly useful. It's what the future of the branded social web might look like, but it won't win many prizes for art direction.