Visiting a blog and leaving a comment is what blogging is all about, it is very very core of blogging life. Those who receive no comments at all tend to give up quickly, no matter how interesting their stuff may be. It is disheartening to receive nothing when you've put so much work into your presentation.

My blog has over 1000 posts and nearly 2000 comments on it right now, which makes it very alive and veryx enjoyable, not just for me but also for all other visitors. When they see that a blog is active, that it draws attention they are more likely to come back.

I must disagree with you on one point, though:

Let them promote....atleast the visit ur blog...

Sorry, but that is the death of a blog. Those who shameslessly drop their name, who post rubbish have indeed visited your blog, but they've taken no part in it. They've entered a standard text just to get a backlink which ups their ranking. The latest updates to Google and other search engines seek these backlinks out and downgrade your blog if they feel that the links are weak or disreputable. That's why we have spam filters, and that's why we should moderate every comment that comes it.

One last little comment, a pet peeve for me: when you have moderated (or open) comments on blogspot, or elsewhere, allow commenters to use all available commenting methods, don't disable the Name / URL function. Not everyone has a Google account or OpenID! You'll only lose out, they won't come back. And, since you moderate, it is easy enough to weed out those you don't want appearing on your blog.