Jackson doesnt have the fanboy following like Lucas does(or had).
Does it matter? You have a different actor playing the role. From a continuity standpoint, is it really that big of a deal?
Now, if he casts Ian Holm in a scene in the later film tying into the LOR Trilogy, I'd see the necessity.
As far as Star Wars is concerned, I understood replacing Ian McDiarmid in Empire, but I didn't get putting Hayden Christiansen in at the end of Jedi. My two issues: #1, Luke had never seen his father before he removes his mask in the Death Star hanger. How would he recognize that the man standing with Yoda and Ben is in fact Anakin?
#2, the entire death sequence with Vader, Obi Wan, Qui Gon, etc makes no sense. Obi Wan and Yoda speak about them becoming "One With The Force" which is why they disappear, yet Qui Gon and Anakin do not. What gives? Furthermore, wouldn't your projection in the force be based upon the moment you became one with the force? So why does everyone else look like their older selves, but Anakin look like he did 30 years ago?