It does sound different, like Shatner's voice in general during the early 1970s. For example, if anyone sees his guest star roles on The Sixth Sense ("Can a Dead Man Strike from the Grave?" from 1972) or The Magician ("The Illusion of the Queen's Gambit" from 1974), t is easy to hear his voice not being exactly the same as it was when he recorded the TOS narration. His TAS narration is not delivered at the same level of "building call to action" as that heard in TOS, and word emphasis sounds different. It would seem Shatner re-recorded it for TAS, or some alternate take from TOS was used/modified (with the aforementioned reverb) for the show.