The sounds in the Star Wars universe are usually very unique and diverse. In the original trilogy the sounds made by Chewbacca and R2-D2 seem to be brand new sounds in each film, meaning that R2 and Chewie don't make sounds in Ep. V that were recycled from sounds they already made in Ep. IV, etc.
However in the prequel trilogy this is not the case. The sounds made by Chewbacca and R2-D2 seem to just be old sounds recycled from the original trilogy, meaning R2 and Chewie only make sounds in the prequels that were recycled from sounds they already made in the original trilogy.
Not only that, but all Wookiees' speech is made up of sounds recorded to represent Chewbacca's speech. The Wookiees don't seem to make any sounds in Ep. III that Chewie hasn't already made in the original trilogy. Humans have different voices, protocol droids as well (C-3PO vs TC-14), so why should all Wookiees speak stock-Chewie-sounds.
Why do the Prequels recycle old sounds for R2-D2 and Chewie (and all Wookiees)? Is there an explanation for this seeming laziness on the part of the filmmakers? Have the filmmakers commented on their decision to recycle these old sounds?