FWIW, I noticed this while doing my SDH subtitling. Since I tried to match each sound to an emotional adverb (yeah, it's terribly subjective, but also a terribly important part of his "speech" for deaf viewers), ROTJ R2 seemed to have a bit of a different personality. The R2 in SW and ESB was a rude wise-ass with good intentions. R2 in ROTJ has a strong pollyanna vibe. For ROTJ R2, it seemed everything was always going to turn out just fine, you'll see. SW/ESB R2 had a lot more negative things to say.