They haven't done that with Luke, though, or Leia.
Like Coco said, Hammil's face did change and differed in all 3 films, and in the case of Leia, the Boushh sculpt requires the hair coming down on the sides of here ears so it's best to sculpt that as was done reather than add it on later, SSC seems not to add Sidesburns but sculpt them on. Even Ford looked different among the films, but Portman has looked the same since TPM, B E A UTIFUL. Other than hair and wardrobe, I really don't see much difference between ROTS and TPM, you could easily get away with it, and Trev nailed her portrait, it's a situation where if it's not broke don't fix it. If Jedi Luke's sculpt could have worked for ANH and ESB, I'd have been for reusing that as well.