Sorry Robert, if people have to create and log into their own blogs just to leave comments on other blogs they are reading... you'll lose at least 90% of the feedback.  The barrier to entry is just to high.  I have to:

1. Read your post

2. Create a blog if I don't have one. (The 90% case)

3. Open a new window to my blog

4. Cut and paste a link from your blog to mine... or at least somehow effectively reference your blog.

5. Post my entry

Compare this to two steps required to post a comment on most blogs that support comments effectively.

1. Read the blog.

2. Stay on the same page and post a comment. 

I guess the basic problem is that not everyone in the world has a blog... nor does everyone want one.  But I DO want to get feedback from people who don't blog.   I do want to engage them in a conversation. 

Sure, the five steps don't seem that complicated, but take a listen to what the social computer users of tomorrow, bloggers of last year (not of this year :-) ), and easily distracted/discouraged from technology teenagers from the Social Computing Symposium had to say. 

Two steps is too much of a barrier to entry for most people today to leave comments. Why complicate things by requiring that we all have blogs? I know there will be more than a few people that disagree with me on this one... but blogging without a comment Field is not blogging to engage in a conversation.  Want to know who a bad blogger is... ones that restrict comments to only other bloggers. :-)