I made an observation recently. Blogs with no nofollow tags are almost all at PR0 after the last update. Some were as high as 5 or 6 last time... I think google is trying to tell us something. You can see a list of old PR's here: http://www.digeratimarketing.co.uk/toolshop/DM_BlogsThatFollow.pdf (not my site) compare with what you get from iwebtool and you will be shocked.
Nothing so shocking as this was made aware to all webmasters by Google's Matt Cutts in his blog long back
Some are, that didn't go to other measures to maintain their page juice. Alot of nofollow websites have remained at a constant PR or even gained rank.
Woah that is wierd.. Why penalize blogs..how about forums? Forums don't have nofollow and there lots links on them.
I may agree to this slightly as I had a do-follow plugin on my blog which got a pr0 for some strange reason. So your theory can be correct.