I expect the FW31 was compromised for an expected KERS release and with the change in powerunit's they felt starting fresh with what they'd leart would be best...
http://www.autosport.com/news/report.php/id/81003
autosport.com
Williams is pinning its hopes on an aggressive new aerodynamic package in a bid to return to winning ways this season.
Technical director Sam Michael told this week's AUTOSPORT magazine that the team's new car would not be a simple evolution of its 2009 design.
"The FW32 is a clean-sheet design from front to back," he said. "It's pretty much brand new from an aerodynamic point of view."
According to Michael, the radical new regulations for 2009 gave the Grove-based squad the opportunity to bridge the gap to the front-running teams, and he believes that Williams's consistency last season is a strong platform to move forwards.
"The fact that we had a consistent car across all of the tracks in 2009, and wiped out a lot of the vices that we had in the previous car, gives us confidence."
Williams also believes in veteran Rubens Barrichello and GP2 champion Nico Hulkenberg the team has a strong driver line-up to help achieve its target of wins.
"Rubens is quite a demanding guy, in a positive way, because he wants to achieve things quickly," explained Michael. "He is unlikely to be around in five years' time because of his age and has a sense of urgency about him."
Hulkenberg is rated as one of the best young drivers around and, after two years at the Oxfordshire team as a test driver, is fully integrated.
Along with Barrichello, who pushed Jenson Button for the title last season, Michael believes the team has its best chance of re-establishing itself as a winning squad.
"The amount of pushing Nico is doing will be good for Rubens," said Michael. "Nico has been quick since he started at Williams and he's been pushing himself very hard."