I recently saw a website which was just launched 2-3 months back.. it was basically a sub domain. It had a 0 pg rank as usual as start, but after some months its directly got pgrank 4??? and that too I checked its backlinks its got no backlink at all in google!
Actually Google updates itself internally daily...while you may not have found links they are there...go do link:http://www.website.com on yahoo and msn you shall see the links Google sees but does not update public for 90 days or so.