I really hate to post on wordpress at because some of the comments do not get approved. I have been posting on do follow Drupal blogs and there is no moderation on a lot of them. I really wish that someone would put together a drupal dofollow blog list as much of the list are wordpress only.
If your commenting is good it will definitely get approved. Can you please share the drupal list here ?
When commenting on blogs, first make sure you have read the posting. Really. Then, say something that relates to the posting on which you are commenting. Make it look like you are interacting in the way the blog is set up for.
It's all about the quality of your comment. If you are just adding blatent SPAM, you'll never get approved. Read the post and add something valuable to the conversation.
regarding few comments above advicing OP to read the article and then post a useful comment which will guarantee approval, i have to say thats not gonna happen all the time with moderated blogs. while all blog owners including myself need comments on their blogs, not every one will welcome a commercial link on the comment. to get a backlink form a blog comment, you need to use youur keyword in the name field and then put the URL on the URL field. since its a commercial link with a commercial keyword, there will be lot of blog owners who will deny the comments or approve the comments but delete the URL. also, wordpress now-a-days is nofollow to begin with unless you make it dofollow manually. drupal is dofollow by default and i have to agree with OP that most of them are not moderated yet