I'm new to this so hear me out... When commenting on a blog for pr, doesn't your comment end up on a separate page from the main page of the blog, which usually has a pr of 0?
Usually your comment end up on some internal page and not the main page. So you can expect a lower PR if any at all. Keep in mind most of the blogs have NoFollow tag. NoFollow links won't increase your PageRank.
the links in the thread i posted before.. in my sig also.. .are all do-follow sites... so would be wise to get posting boy.. i have used this list for a while now and some of my other sites have shot up PR alot quick than expected.
Your observation is correct. There is a difference between domain PR and page PR. Only by leaving you comment on dofollow blogs with high PR values, you can expect some juicy PR returns. Nevertheless, leaving comment on either high or low PR site that related to your niche will still bring good amounts of traffics.
each blog article has its own permalink and has its own PR which can be zero to begin with but increases over time. so the PR transfer is based on the PR of the article page itself and not the main domain. one good thing about blog is, if it is a busy blog and has good PR main page, permalinks will have their own PR over time