Google isn't a person? Haha, your correct in what you are saying, the spider can detect where on the website the link is placed, a backlink in the main content body will have more 'juice' than a comment backlink. You should also consider the fact that most blogs have nofollow comment backlinks and if your being linked too in the content body, you would assume the author would dofollow the link, making it much more beneficial. Blog commenting is still a great way to build backlinks - however the quality of guest post links / links-in-content is much greater
There are benefits to commenting on blogs besides link juice. You could develop some wonderful relationships and also support a fellow blogger.