Don't forget that some drivers pay to be in F1, and their only reason in F1 is to pay for a struggling team.
Alex Yoong was an example last year; certainly Enrico Bernoldi was one last year as well. I'm not too sure about the Class of '03, though.
Heck, I'd drive an F1 car for a year on a U.S. minimum wage ($5.15/hr) if the team took care of all my insurance, flights, food, lodging, a dozen free race passes, etc. I doubt if Kathy would go for that, though.
Salaries in F1 followed the direction of other professional sports; around 1990 or so, Ayrton Senna was demanding ~$1million a race (16mil/year); in the mid-80's it was $3 million a year for the likes of Prost and Piquet. Lauda made about $1 million a year in 1982 or so.
In the mid-70's, $200,000-$300,000 was a superstar driver; and so it gets less and less as it gets older. Estimates were that in the 1950's, you made about $20K-$50K as year as a professional race driver; and that meant more races (sports-cars, touring cars, non-championship events, etc.)