This is good news.
Anyone using 301 redirects to redirect from a free Wordpress account to a registered domain name, or in order to tidy up site structure shouldn't be disadvantaged any more.
I think the way that Google assesses whether or not to pass juice probably doesn't differ between whether the mechanism is a standard link or a 301 redirect. I would guess that it assesses whether the anchor text is appropriate for both the linking page and the target page given the content of both, and whether the link profile overall of the target page is consistent with the topic of the page.
When the 301 is first put in place, Google may compare whether the old URL and new URL are about the same topic, but I can't imagine it doing this on a regular basis afterwards - well curated content can change slightly over time and Google isn't going to take snapshots of every page every minute of every day indefinitely.