Its helpful no doubt.. but many ppl have started spamming using the same method. **Offtopic: Your sig (last link) is broken
yes it's very much feasible to put you comments on blogs as it may help in increasing you customer range as well as popularity in the market. Your range increases and you can help or encourage the person so it seems very much feasible to post comment on blog.
I can't think of anything more depressing, if 99% of those are spam or illiterate garbage. Points 3 and 4 on that page basically seem to be saying the same thing: getting indexed depends on getting backlinks, after all. There's no reason not to post comments on blogs, when you actually have something to say. I don't know that it matters whether or not they are actually related to your website's topic, or completely irrelevant. That will make no difference at all to whether or not the link gets indexed.
if you're using blog commenting to do traffic generation, it helps if you have some useful content in your blog comments. yes, even comments can have content. if you're commenting for the sake of commenting, any seasoned blogger will be able to tell that you're doing it purely to pull traffic and will delete your useless comment without a moment's hesistation. i'd suggest to aim to provide value to the blogger and his/her readers first, and get the traffic as a side benefit. if you're planning any potential JVs with the blogger, you dont want to piss them off by spamming their blog with junk.