There was no salary cap in 2010. Some teams, like the Bucs, decided to go cheap on the year. I don't have the figures in front of me but I believe some of them spent less than what would have been the salary floor.
EDIT: I clicked your link provided. The salary floor in 2009 was 107 million. And based on those figures in your link, 17 teams spent less than that in 2010.