ACFT SLOWS WHILE CLBING FROM FL210 TO FL230; 30 KIAS. CAUSES LOSS OF SEPARATION FROM ACFT FOLLOWING.

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ROUTINE FLT AT FL210; ENCOUNTERED LIGHT TURB IN AND OUT OF CLOUD TOPS. REQUESTED FL230 TO GET ON TOP. ACFT WAS HEAVILY LOADED AND IN AUTOPLT CLB MODE; SLOWED FROM 190 KIAS (CRUISE) TO 160 KIAS (CLB) AS WE PASSED THROUGH FL220. ATC ASKED WHAT OUR IAS WAS AND I REPLIED '160 KTS IN THE CLB.' ATC REPLIED 'YOU'VE GOT TO TELL ME BEFORE YOU REDUCE YOUR AIRSPD THAT MUCH SIR; BREAK; ABC XXX (COMPANY ACFT) GIMME A GOOD L TURN 30 DEGS AND REDUCE YOUR AIRSPD AS MUCH AS PRACTICAL.' THEN LATER AS HE HANDED OFF 'ABC XXX' HE SAID 'THANKS FOR YOUR HELP; IT SAVED ME FROM MOUNDS OF PAPER WORK.' WHEN HE HANDED US OFF; I APOLOGIZED FOR THE SUDDEN LOSS OF AIRSPD AND TOLD HIM IT WAS A NORMAL CONSEQUENCE OF OUR HVY ACFT CLBING FROM FL210 TO FL230. HE SAID IT ALL WORKED OUT BUT THAT HE SAW A 40 KT LOSS OF GND SPD IN 2 OR 3 SWEEPS CAUSING COMPANY ACFT TO CLOSE IN ON US THEREBY REDUCING SEPARATION. SINCE IT IS PERFECTLY NORMAL FOR US TO LOSE THAT MUCH AIRSPD WHILE CLBING; I'VE NEVER THOUGHT OF RPTING IT TO ATC AS A CHANGE OF TAS PER AIM 5-33; A;1(E). I WONDER IF YOU MIGHT ADDRESS THIS ISSUE IN A FUTURE ISSUE OF CALLBACK AND ENLIGHTEN US ALL WHETHER OR NOT WE SHOULD ALWAYS RPT LOSSES AND/OR GAINS OF TAS IN CLBS AND DSCNTS.