Not sure how you would go about adding torque settings to an impact mechanism... (perhaps that is why the tool makers have not offered it yet!)
For smaller screws (say 3mm - 4mm or 8 gauge and thinner) and in the 3/4 to 1 1/4" length range, (i.e. screws that are trivial to drive with a drill driver) then I would agree that there is no real advantage over using a ID in place of a DD. However, having said that I have not had any difficulty in actually using a ID for these. (very small screws get harder due to the lack of a very slow rotation rate).
I don't think I have ever had a screw head actually shear off completely (although see caveat below). With larger screws I find I am less likely to wreck a head with cam out/spinning the bit in the screw when using the ID due to requirement for less force to be applied to the tool. In fact I probably have killed more bits than screws. Mild steel bits are useless in an ID. The wiha / vera diamond impregnated ones work well, although the bits will shatter from time to time. Actually the Screfix Erbauer packs of 25 bits work very well - hard enough to take the abuse, but not quite as hard as the posh ones and hence slightly less likely to shatter.
However the caveats are: you must use decent quality screws, and also good quality bits that fit the screw head very well.