If it worked that way, then adding a blog to your bookshelf would be meaningless. You can make it work for you the way you want it to by adding every blog in the blog list to your bookshelf.
I find the way it works elegant. I only follow (have added to my bookshelf) select blogs I've found to be good sources for me. And I'm sure it's helpful to those folks who have limited interests due to specific diets -- vegetarians, vegans, diabetics, etc.