In general we don't record VO for every instance in the Epic, mainly because the speed that we need to release updates doesn't mesh well with the longer lead-time that VO recording requires. That said, the instance that covers the Last Debate is already very, very long (ThePinion has been sending me quotes from World Chat with people wondering if the instance is eeeeevvvveeeerrr going to end!) and adding VO generally slows down each line by 3x or 4x. There's also the issue that some of the characters that are involved in that instance are performed by the same voice actor, and while we've definitely had actors talking to themselves it's a good thing to avoid if we can.
So while I enjoy having VO in instances, it's not always the best thing to add in instances that are especially chatty.
MoL
That was not the case with the Meduseld/Edoras quests though. I agree that the instance is very long and part of the reason is that I don't pay too much attention is because there is no VO... It is just one instance at least though. I wouldn't mind a longer instance if that is an exception and not a rule, which is the case. =)
I don't see an issue with some of those characters being performed by the same voice actor. I remember talking to many of the rangers in Dunland and most of them, if not all, having the same voice actor. We've also had characters changing VO actors throughout the epic story, in some cases the change was very abrupt (the voice changed a lot) such as Horn's voice from Great River to Rohan, the blackroot vale brothers from South Ithilien to Old Anorien, many of the rangers of the north... for me that is something I would notice more than two NPCs having very similar voices. But that's just my opinion.