As Richard puts it:
In an ideal world, though, no weblog would have comments enabled, but everybody would have their own weblog. You remember that old cliché, the freedom of the press goes only to those who own one. Well, there is remarkably little stopping you from owning one these days. MovableBLOG: The Real Problem with TypeKey
The rest of Richard's post is actually about some problems with TypeKey, plus the de-centralized nature of weblog comments. I find that short comments that I make on other sites are generally forgotten (by me, in any case). If I have something longer to say (and this sometimes is only realized as I start typing) I'll make a post about it and point at the entry.