Where did you read this? I do not think this is the case at all... Camry, ES and Avalon all have the same "drag and drop" V6 and 8AT. Gear ratios on the 8AT are the exact same, and they use the exact same ATF. Throttle input/ECT-i could be tuned differently, but I highly doubt that. It is a super smooth and powerful powertrain by itself - no need to make it any better or different for Lexus, IMO.
I am pretty sure quite few of the reviews on either Avalon or Camry TRD were complaining about transmission logic and mentioning how much better it is in Lexus. Maybe I can find them over the weekend, did not have time yet, but I clearly remember it just dont know what car was reviewed.