as far as i guess it doesn't matter.. however the link you get from comment on the blog is dofollow or nofollow that matters.. dofollows matters most!
The pagerank of the blog could matter. Certain people place the list of their top commentators ( do follow, and therefore a link from the home page) Post pagerank could also matter, especially if you're commenting for a backlink on it.
I normally don't bother to see pagerank of the blog I am commenting on. What matters is you have great comment that provokes blog owner as well as other readers to visit your site. Blog comments can often bring you invitation for guest posts as well.
People get too hung up on PR. The PR you see in your Google Toolbar is already out of date. The Toolbar PR could say the site has a PR4, when in reality, it might be a PR0 because Google just implemented an algorithm change yesterday that discounted almost all of their inbound links. Yet the Toolbar PR was last updated 3 months ago. You don't ever know what the PR of a site. The Toobar PR is a snapshot of what that site's PR was weeks or even months ago. It's like looking at a star in the night sky. You see the star there, but it may have supernova'd or burned out years ago. You're seeing the residual light of the non-existant star as it passes through space from light years away. Instead of concentrating on the PR of the blog you're posting your comment on, concentrate on whether or not that blog is relevant to your site. I would rather have a link from PR0 site that is very relevant to the my page they are linking to than to have a link from a PR4site that is not relevant at all to my page they are linking to. So what if it passes me less Page Rank... PR is just 1 of over 200 factors that are considered when Google ranks a page for a particular keyword phrase, and it's even considered a minor factor at that. But there are several very important factors considered in the ranking algorithm which revolve around the relevancy of the page which links to you, the relevancy of the link text they use to link to your page, etc. Forget about PR. Write unique and compelling content that people want to read. Look for ways to get links from relevant sites with relevant link text. And life will be good...
You can write good anchor links with your keywords in them on a page [blog] that is optimized for your target keywords »plus« you can write great content. As one person noted the PR is a "changeling", but at the same time it just may change for the better in the future, and you already had your great anchor tag on it back to your site. You never know. You do not have to choose between good SEO and great writing if you are good at both.