You're right. I wonder if the difference is that Charles has shown enthusiasm for the Royal role and was thought to be frustrated at the long wait for the top job? William, on the other hand, has often been labelled 'the reluctant royal'.
Regarding Harry's inheritance, it doesn't look like Andrew, Anne and Edward inherited several hundred million between them (although maybe they did) so I don't know why Harry would get that much. And I thought everything was left to the heir to avoid tax and then the heir is supposed to carry out the late monarch's wishes. I could see Charles and William discussing and agreeing it between themselves, deciding how much to give Harry, and dishing out the money over time and with constraints (A & L's education, health care and housing, perhaps a contribution to security, etc).