I tried watching the newer movies, and the cognitive dissonance from remembering the old voices but hearing entirely new ones was a bit frustrating. --- "Whoa! Heads up, detecting high levels of space chickens." "No! Space chickens are a surgeon's worst nightmare."
Well, yeah. He's 10 years old. That's what 10 year olds are supposed to sound like.
The director wanted the voice to be deeper because he thought that was what 10 year old boys sounded like, but Veronica Taylor (Ash's voice actress at the time) proved him wrong by bringing in a recording of her 10 year old nephew, and thus was allowed to make the voice much higher.