It works for Earth troposphere pressures (200-1000 mbar) which overlaps the cloud layer. It is slightly off within the cloud layer. Anyway you seem to be proposing an alternative reason there is no affect of CO2 on venus's temperature, and thus no evidence for runaway greenhouse effect.
Well, I always understood that the greenhouse effect was this: shorter wavelength radiation crosses the atmosphere in spite of any CO2, gets absorbed by the ground, is re-radiated as infrared, and this is prevented from escaping by the CO2.
If so then Venus may not have a greenhouse effect because the shorter-wavelength radiation gets reflected by the clouds without being converted to infrared, and therefore does not get trapped by the CO2. But I am just, er, academizing about it.
