There are notably no female Nords, Orcs, or Redguards anywhere in the Shivering Isles, not even as generic NPCs. Apparently, Lynda Carter and Gayle Jessup (who respectively voiced the female Nords and Orcs, and female Redguards) weren't available when voice recording for the Shivering Isles expansion began.
Also, while most of the males of the ten playable races (barring only the Bretons) have new dialogue recorded for Knights of the Nine, only the females of the Imperial race have new dialogue as well (which is strange, since the female Bretons have the exact same voice actress and voice type as the female Imperials, yet don't have any KotN-related dialogue assigned to them). Some of the plug-ins try to hide this by recycling voice clips from already-existing NPCs when the appropriate voice actor isn't available for recording, but it's fairly obvious at times when the dialogue was lifted from someplace else in the game.
The Other Darrin: Uriel Septim was played by a different, unnamed local actor in Daggerfall's opening cutscene, in Oblivion he is played by Patrick Stewartnote probably chewing up a chunk of the voice acting budget: there are many, many characters, and few voices.
Talking to Himself: An unfortunate side effect of Bethesda's decision to have the game be fully voiced, while hiring only a handful of actors to voice over 1000 characters. It's quite possible you'll be hearing two NPCs conversing to each other with the exact same voice!
One VA for all Imperial Males, one VA for all Orc and Nord females, one VA for all Orc and Nord males and so forth.
What Could Have Been: In the other direction, the initial descriptions of Cyrodiil in Redguard/Morrowind were much stranger and more fanciful than what ended up in the game, featuring river dragons, singing priests covered in robes made of moths, and living topiaries of the dead emperors that could speak and move their bodies with the help of birds. The retcon was only vaguely alluded to within the byzantine Mythic Dawn Commentaries, though it's more explicit in the more lore-savvy Skyrim, incorporating an extracanonical explanation written by the writer who had described much of the original Cyrodiil to begin with.