Another stupid transponder question

The other day, after launching from Iowa City, Cedar Rapids Approach (CID)
gave me my squawk code, as usual.

My usual procedure is to read back the squawk code as I punch it into our
Garmin 327. (It's got keys to punch, rather than dials to twirl.) This
time, however, I punched a wrong number, and had to re-enter the whole code,
which added a second or two to my reaction time.

Before I could read it back to the CID controller, he had moved on to
another plane. The radio was solid for another minute, until he came back
with "N56993, radar contact 4 miles north of the Iowa City Airport..."

Which led me to question why I ever read the code back in the first place?
Since the controller can obviously see the code on his screen, he certainly
knows that I have complied with his instructions.

So why do we read it back?

*Does* everyone read it back?

I think it's almost more of a tradition than a real procedure. I suppose
it's possible for someone else to have heard his instruction, and for *them*
to have keyed in the code -- but reading it back doesn't really prevent this
scenario from happening.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"