Doubling a quantity isn't exponential? Try telling that to a rabbit. I'm using "exponential" in a relative sense. Adding one apple to a set of one creating a set of two wouldn't be exponential....adding a planet with life to a set of one is going to end up equaling a hell of a lot more.
I've been looking for adjustments in the traditional equations to account for the recent Hubble discoveries and haven't ran into anything as yet, but I'm certain the probability numbers are going to have to be re-examined based on these discoveries and the growing list of proven planets in other solar systems. Until recently, they couldn't even be certain other sloar systems existed much less other planets.