The key phrase for me from The Art and Science of Blogger Relations, an ebook from Brian Solis, is this:
It’s the difference between commission and fixed salary – it’s all related to the ability to sell a story vs. tell a story. (p. 49)
Think of the role of the PR practitioner as storyteller, not as sales representative.
In this (and in so much of the territory covered in the book) there’s little to distinguish blogger relations from media relations. Especially when many of his blogger examples, like Chris Anderson, are well known reporters.
PR Studies 
Richard, you’re exactly right. At the end of the day, whether it’s media relations or blogger relations, it’s simply about people reaching out to people. Ultimately, it transcends into conversations…which look less like pitches and messages and more like discussions.