Once you get your authorship working, no one wants to mess around and change URLs. Some don't like to mess around even if the authorship is not live in the search results, in fear changing it might break something. This is even more so now that there was a reduction in authorship display in the results.
One question I get a lot from more advanced SEOs is should I use the numeric or custom/vanity URL from my Google+ page. Should I use the root or /about or /post URL as well? The answer is, it does not matter.
Google's John Mueller went on record about this topic this morning on Google+ saying:
I've seen this come up more since custom/vanity URLs for Google+ profiles have become more popular. Authorship works fine with vanity profile URLs, it works fine with the numeric URLs, and it doesn't matter if you link to your "about" or "posts" page, or even just to the base profile URL. The type of redirect (302 vs 301) also doesn't matter here. If you want to have a bit of fun, you can even use one of the other Google ccTLDs and link to that.
So there you have it, concrete information from Google on one of the scary topics to touch on.
Forum discussion at Google+.