So basically, Williams are now heavily reliant on their drivers bringing in sponsors, as opposed to the team itself, bringing in the main sponsors. This is not a good strategy UNLESS, one of the drivers owns/runs the team.
I still believe that the main problem with Williams is money. If they could employ some top sales staff to bring in some sponsors (which is not easy when the car is performing so badly) to increase revenue, which in turn can be used to employ some top end engineering/design staff, who in turn can produce a better car.
If you go back to the mid 90s when Williams had a comparable budget to other leading teams (excluding Ferrari...who had a ridiculously big budget), other teams were thinking of ways to increase future revenue. McLaren decided to associate their name with Mercedes and push their brand (the name McLaren is synonymous with Mercedes - a huge name in car production worldwide). They also built a huge production facility in Woking which would be used exclusively to produce commercial vehicles (for profit).
Imagine, if Williams, during their heyday had produced commercial vehicles, endorsed by Mansell, Prost, Senna, Hill, Villeneuve (these are some of the biggest names in the history of F1) and even Montoya...they would've made a small fortune. Ferrari made full use of MSc's name. Vodafone are making full use of Hamilton and Button's names. Williams failed to capitalise on their assets.
To be honest, when you look at things from a commercial stand point, Williams are clearly an old-school team, who are unable to compete against teams who are more commercially astute. For me, it all comes down to money and Williams are completely to blame for not having enough of it and being subsequently forced into hiring rent-a-drivers, who are unable to extract the maximum from the cars.
I remember, reading a comment on these forums stating that an F1 team should not be run as a business. Well, the Williams F1 team is living proof of what happens when a team is not run as a business.