There's no reason USAF shouldn't have GPS approach capability in a primary trainer. As far as airmanship, I agree with you; flying an LPV can be done by any stick monkey who's practiced enough ILS or non-precision with arcing, etc.
But in a primary trainer that's expected to teach students about versatility and ADM, taking away RNAV takes away options from the front and back seater. That's a lot of fields that you can't go to in IMC. Personally, its more about giving those crews options.