Say that I'm selling a book. I work really hard to get a world famous blogger to put a link on his blog post, and he does it. Now say I didn't work that hard, and just left my link on the comment. Does google rank the link with the same amount of importance?
The would be ranked the same assuming that both are do-follow and that they are both the same contextual wise. If the actual blogger link was a do-follow and the comment link was not then definitely the blogger link is better.