Seth Godin is providing advice on how to blend in with the natives:
A blog is something you have (unlike a Facebook). And blog is also a verb. As in, “I have a blog, this blog, which you probably found by googling me. I blogged about Facebook (which I’m on but don’t use often). I don’t IM, and I’m impossibly lax about friending people.”
It is easy and pointless to sneer at those who don’t get it. Much more interesting to apply the principles of language maps to chart where the invisible boundaries come. One of those boundaries forms around “a blog” used to mean a part rather than the whole: “I wrote a blog” rather than “I have a blog”. I have started to hear the former usage – which tells me that too many people are trapped on the wrong side of an iron curtain they do not know is there.