i can't remember the source but outside of maybe 6 drivers in indy car, all the rest rely on what money they can bring to the table to help get a drive, sponsorship is far more important than it is in NASCAR, you only have to look at the driver earnings for last year, dario's earnings wouldn't place him in the top 50 in the NASCAR table, that lack of prize money's reflected in the teams as well hence driver sponsorship being so important.
mush as a hate to say it i think dario may struggle this year relative to previous years, there's less ovals which have been his strong point whilst drivers like power will benefit from the greater emphasis on road courses. given a bit of luck someone like wilson who, unlike barrichello, knows the courses may be able to make an impression as everyone gets to grips with the new car, especially early in the season before the big teams resources start to take effect.