I agree that self-voting comments is kind of scummy, especially since it's one of those "Nice!", or "Followed, pls follow back!" kind of comments. But self voting is completely legitimate, in my opinion. If you think of your blog similarly to a company, such as a newspaper, or whatever the topic of your blog might be (there's a niche paper for whatever), then you are the CEO of this endeavor. And you need a salary, which is proportional to the entity's success. This success is only what it is due to the work and research and arguments you put into your posts. If you think of comments similarly, it's like giving yourself money just for talking to business partners, even if no deal is reached.
Hope my metaphor is helpful to explain my position on the issue :)