I think part of the problem to the outside world is that Williams, rather like McLaren, consider the car to be much more important than the driver. I remember reading once that Ron Dennis regretted the amount he paid to Senna and Prost and would rather have spent the money improving his cars. I think Williams hold this approach too, which is why you tend to get quite robust individuals who turn out to be the greatest successes in Williams cars. Just look at Jones and Keke Rosberg, probably two of the most favoured Williams drivers. I think Nico has learnt a lot from his father on how to drive for the team. Unfortunately Wurz lacked the speed to compete last season, and I think whilst Williams would like to have kept him on, it would have been an awkward situation to have him lurking around whilst Nakajima took his seat. Also it has meant Williams can bring in Hulkenburg to groom him into a replacement for either of the current drivers should one leave in 2009.
One thing though, it means Honda now have I think the oldest driver line-up on the grid, which is good for experience, but not for the future.