I've been waiting for Marty Mayes to weigh in here, since I am in complete agreement with his contention in another long thread (maybe on AOPA) that many pilots parrot back too much meaningless information when a simple acknowledgement will do.
Here's what the AIM says regarding readbacks in 4-4-6:
ATC Clearance/Instruction Readback. Pilots of airborne aircraft should read back those parts of ATC clearances and instructions containing altitude assignments or vectors as a means of mutual verification. The readback of the "numbers" serves as a double check between pilots and controllers and reduces the kinds of communications errors that occur when a number is either "misheard" or is incorrect. 1. Include the aircraft identification in all readbacks and acknowledgments. This aids controllers in determining that the correct aircraft received the clearance or instruction. The requirement to include aircraft identification in all readbacks and acknowledgements becomes more important as frequency congestion increases and when aircraft with similar call signs are on the same frequency.
EXAMPLE-
"Climbing to Flight Level three three zero, United Twelve" or "November Five Charlie Tango, roger, cleared to land."
2. Read back altitudes, altitude restrictions, and vectors in the same sequence as they are given in the clearance or instruction.
3. Altitudes contained in charted procedures, such as DPs, instrument approaches, etc., should not be read back unless they are specifically stated by the controller.
c. It is the responsibility of the pilot to accept or refuse the clearance issued.
I don't see anything there about altimeter settings. Yes, you can make the argument that you should read back EVERYTHING, because they might catch it if you make a mistake. But that's not what the AIM says, is it? Perhaps cutting down on noise on the frequency counts for something too. Sure, question if you think you misheard it, but if you heard the numbers clearly, why parrot it? For those who do NOT read back altimeter settings have you ever, even once, been asked to read it back?
Plus,as previously pointed out, the altimeter setting you're given should be pretty close to the setting you're already using, or the one on the ATIS or AWOS, or the one the controller's given to the ten other airplanes who check in. If it isn't close to what you expect, ask, or get on the ground fast, because you might be flying into a hurricane with precipitously falling pressure.
Yes, an alt. setting is only four words, but that's more than "with you," and "standing by," and almost as many as "any other traffic please advise."
Jon