To ionize the air with laser light it take very large energy densities.
Yes, but I would think that the 1016W lasers people were talking about might ionize air, which would cause pretty severe attenuation. Smaller lasers aren't going to ionize air, and thus will be attenuated much less.
From his post, that's my understanding as well. But this would mean that 'low-power' lasers are EXCEPTIONALLY efficient in the atmosphere. Given the coherence of the light frequency I can buy that.