FYI What is an update? Google updates its index data, including backlinks and PageRank, continually and continuously. We only export new backlinks, PageRank, or directory data every three months or so though. (We started doing that last year when too many SEOs were suffering from “B.O.â€, short for backlink obsession.) When new backlinks/PageRank appear, we’ve already factored that into our rankings quite a while ago. So new backlinks/PageRank are fun to see, but it’s not an update; it’s just already-factored-in data being exported visibly for the first time in a while. http://www.mattcutts.com/blog/whats-an-update/
That's been known for eons. Some people still think that only when the 'update' goes public their rankings will magically shift.
They do update positions all the time. BL and PR updates happen less often and can cause bigger shifts in the rankings.