The 13" MBA has a 54Wh battery, and Apple claims it get 12 hours of "wireless web" use. The 13" MBP has a 72Wh battery and claims 9 hours of "wireless web" or "iTunes movie playback". In practice, people find the Apple claims fairly reasonable.
While that does not prove how precise or accurate their projections are, I don't think they are absurd. Software-based monitors of power consumption on MacBooks show variation between low single digits and low teens under light use, and shoot up dramatically if you are doing something intensive.
The 13" MBA has a 54Wh battery, and Apple claims it get 12 hours of "wireless web" use. The 13" MBP has a 72Wh battery and claims 9 hours of "wireless web" or "iTunes movie playback". In practice, people find the Apple claims fairly reasonable.
While that does not prove how precise or accurate their projections are, I don't think they are absurd. Software-based monitors of power consumption on MacBooks show variation between low single digits and low teens under light use, and shoot up dramatically if you are doing something intensive.