Personally, I see my blog and Twitter feed as two very different types of communication. Twitter, etc is great for quick little comments, sharing links, short updates of what's going on my life, questions to friends, etc, whereas my blog is good for more in depth posts like technical projects I'm working on, longer opinion pieces, tips and tricks, etc.
Similarly, I hate reading individual's blogs that simply talk about their boring day to day life, but 140 character chunks of that stuff is ok. On the flip side, there's no way to fit anything substantial (like my typical blog post) into 140 characters.
"A stand-alone commentator can't keep up with a team of pro writers cranking out up to 30 posts a day."
My approach is to not to subscribe to these kind of high volume "professional" blogs, but rather lots of little low traffic blogs.
I figure if there's something truly important posted on one of these mega-blogs my peers will inevitably post about it (on their blog, Twitter, or Facebook) and I'll find out about it anyway. Plus I'll see a huge variety of posts and little gems that never make it up to the big guys, rather than a zillion "xyz company released abc cell phone" posts on Engadget. I'm a gadget fiend but that shit gets old after awhile.
So don't let Wired and the mega-blogs discourage you from blogging. If you write something interesting the big guys will link to you anyway. My blog has been linked to from Slashdot, Daring Fireball, Ajaxian, TUAW, etc over the last year, and I only post about once a week when I have something I think is at least moderately interesting.