^ Absolutely. People's voices change. I don't sound exactly the same as I did even ten years ago.
As for the big Nimoy, as Trevanian
also alluded to above, I always wondered if he was maybe speaking around a set of dentures and it subtly affected how he sounded on film? Alternatively, I do know that he's spoken about how in TOS he always tried to act it as if English was a second language for Spock, and therefore he said the lines in a somewhat more "formal" manner than some of Spock's ship-mates (notably he actually hits British pronunciation on several words), something which Nimoy essentially stopped doing during the movie era.