In Pd, if you implement a fade using [line~] into [*~], you get one that is linear in amplitude, which sounds like it starts out slowly and speeds up very quickly. If you put [dbtorms~] inbetween and adjust [line~]'s args, it sounds more like a constant fade and you could say it was "linear in dB" or a constant dB/sec fade. There's nothing exactly like that in either REAPER or Soundforge--their audio-tapered curves still speed up as they get softer. Automating the track fader in REAPER shows something similar. In the following snapshot, the automation line on the bottom track is controlling the track fader, and the vertical red marker lines mark the points where the signal drops another 6dB from the previous marker. See how the markers get closer and closer as the fade progresses? That means the fade is speeding up in terms of dB/s, despite being controlled by a straight line between two points.

Assuming that REAPER and SoundForge cater to the way the vast majority of people hear/use fades, the constant dB/sec fade must not be considered useful in most cases. If I'm right, why would that be?