Not sure if those are blogs... No permlinks to 'entries' on the ones I've seen.
I disagree. example:
http://www.plurk.com/p/1oyv7
(open the full plurk, near the bottom click "plurk page" - it's a permalink)
That link would be comparable to a particular blog entry, yes. This, though, is your main page:
http://www.plurk.com/user/jtsage
In looking at that page (and the html code), the 'plurks' don't have permlinks listed. If you click on them, then you will get the permlink for each, but they aren't there until you take some action. Now that I know what I'm looking for, even though the permlink isn't visible right away, there isn't anything in the rules saying that this is required, so I'd tend to say that these are as much blogs as Twitter...