Okay, that's your view on it according to your own way to "play the game". In my experience this is what love is all about - if you'd listen in on phone calls between my husband and me when he is away on business trips, you'd hear the same from us... maybe our game is different from yours but IMHO Charles' and Camilla's game is quite similar to ours....
As for the truth: I think after seeing Charles and Camilla for two years now, 18 years after this phone call and two years after he put "that ring" on her finger, I believe they still adore each other and she still tells him what he wants to hear.
While "poor dumb little" Diana could have done the same and still be his princess: be interested in his work, tell him that he is wonderful, talk him into sleep, miss him when he is gone and look forward to seeing him again - feel that and communicate that to your darling and he will be happy (at least my husband is and Charles does not seem to be unhappy either...)
I think that Diana did not much after she had married Charles to make him happy. Even that famous birthday "gift" of her dance at the Royal opera was something she must have known would annoy him but present her as a beautiful and talented lady in public. If she really had loved him she would have tried to understand the pressures of his life and gone about finding her own place there - even if it meant to wait for some months till he had more control over his appointments and could make time for her. Her marriage to him in terms of Royal pre-planning was rather sudden, so of course he was fully booked for the next months - including time he wanted to spent with his friends or playing polo or going hunting or visiting a gardening show. If it is true what has been written, that she thought he should cancel these plans in order to be with her, then she did not understand that much about men. Married men are normally pretty willing to take their bride with them to their private pursuits or present them to their friends. But they were obviously very different in what "fun" meant to them. And if Diana had not been impressed by his future crown so much, she would have seen that he was not the guy for her....