You're far into the speculative left field with that...you don't know what you're talking about.
ATC has proceedures. Reporting altitude changes is a proceedure, and in this case, really a courtesy. ATC and the FAA does not have an inherent distrust of mode C. Where you came up with such a ridiculous idea, one an only guess.
I can just imagine an ATC version of the Verizon guy, constantly saying "Say your altitude now." "Can you tell me how high you are now?" "Now?" "How about now?" "Say altitude now." Gee wilbur, it might have changed in the last ten seconds, how about now? Sir, I'm going to need you to give me a blow by blow account of your altitude because I have a deep distrust of Mode C. I actually lose quite a bit of sleep over it.
Get real.
XXX, descend and maintain flight level three three zero.
Cleveland, XXX descend and maintain flight level three three zero.
Cleveland, XXX is leaving flight level three five zero for level three three zero.
Thank you.
Cleveland, XXX is now two hundred feet into the descent below light level three five zero, descending three three zero, with eighteen hundred feet, no, make that sixteen hundred feet to go now.
Roger.
Cleveland, XXX, we're showing flight level three four four and sixty six feet. What altitude are you showing for us?
XXX, Cleveland shows you flight level three four zero.
Cleveland, roj, that matches, we're now two hundred feet below that, descending three three zero, doing three seventy five knots.
Roger.
Cleveland, XXX is three three five, descending three three zero, my shirt is white with blue epaulets, I am five foot nine and three quarters, I have brown hair, blue eyes, and prefer blondes who can speak czech, and my sign is scorpio.
Roger, XXX
Cleveland, XXX is almost at three three zero, I nearly levelled there briefly just a little early, leaving three three three for three three zero. Speed has increasesed slightly from my previous report, and my dislikes include people in Starbucks who order more than two cups of lattè and change their mind at least six times.
Roger, XXX.
Cleveland, XXX is level at three three zero, plus five feet.
Roger XXX, Cleveland shows you level three three zero, thank you for keeping me informed. I have an inherent distrust Mode C, your reporting has helped immensely.
Cleveland, XXX. No worries. We are now one hundred feet high and wish to advise that it is my copilot's fault, but are returning to our assigned altitude.
XXX, Cleveland, thank you.
Cleveland, YYY with emergency traffic. Five minutes ago we experienced left wing separation and have departed our assigned altitude.
YYY, Cleveland, understand you are no longer maintaining three seven zero. Say intentions.
Cleveland, YYY is unable to maintain controlled flight, and estimate terrain impact in two minutes thirty seconds, presently descending through flight level two two zero.
YYY, understand wing separation. Understand you plan on striking the ground directly beneath you, is that correct?
Cleveland, YYY, that is correct.
YYY, Cleveland, roger. Say altitude you intend to terminate this flight.
Cleveland, YYY, we believe terrain elevation to be five thousand.
YYY, understand your descent will stop at five thousand. Be advised if you intend to go lower, and also be advised my radar stops at one five thousand.
Cleveland, YYY understands, we will maintain five thousand upon impact.
YYY, cleveland, say altitude now?
Cleveland, YYY is passing one seven thousand, descending five thousand.
YYY, Cleveland, stand by to copy center number regarding altitude deviation.
Cleveland, YYY is unable, and cockpit pen has been pinned out of reach due to centrifugal force. We're sorry about not reporting leaving altitude earlier, we were unable to break through the traffic.
YYY, Cleveland, altimeter 29.96. Advise centrifugal force and not centripetal. Understand traffic, but understand I have an inherent distrust of Mode C. Say altitude.
Clevelad, YYY is passing one three thousand, corrected centripetal. Altitude has been fairly spot-on so far.
YYY, contact next controller on 133.85.
One three three eight five, good day sir.
Cleveland, YYY checking in niner thousand descending five thousand, with second wing separation.
YYY, Cleveland, good day, understand second wing has left you. Be advised I'm unable five thousand. For now, descend and maintain seven thousand. Say altitude leaving.
Cleveland, YYY is six thousand three hundred, unable seven thousand, with request.
YYY, Cleveland, go ahead with request. YYY? YYY?