This code snippet:
(defadvice svn-status-update-modeline (after svn-update-diff-hl activate)
will get diff-hl'ed buffers refreshed after SVN commits originated from svn-status mode. Due to hacky nature of it and psvn.el being some 3rd party thing, I'm not entirely sure if it could make a good pull request. Yet I think it is for the very least README-worthy.
It was bugging me big time, so someone might want it too.
Should be useful, thanks.