Wouldn't it be annoying if you selected somehting like "Let's go over here" and then you heard a voice saying "hey, let's go over here." Wouldn't taht get really redundent over a while, because it would be the same dialoug twice. MAss effect convo wheel and heavy rain were the only two systems to get this right.
Well, yah... the VA wouldn't be verbatim what the rather limited sentences are that show up as your options. That would be the right way to do it, however... see below

Because there are 10 playable races of both genders. Cost and disc space requirements would be insane.
^Because of this lol. That's a LOT of recording. A lot doesn't even begin to cover it. Take ALL the dialogue in ES:V and multiply it by at least 21, that's at least how much it would be.
Not possible. The goal of Skyrim is to create your own character and see the world through him. Voice is one of those stuff that clearly defines a character, and it greatly limits your imagination
it IS actually physically possible, just effectively insurmountable and not worth the time and cost investment. My imagination is in no way limited by cmdr shepards voice. On the contrary it makes the story more involving.... so long as it's done RIGHT.... which means not only having male/female of EACH race reading every single different line, but having different contextual changes to the lines as well exponentially increasing the VA even more
Too much memory, would destroy the series if implemented and Skyrim is a 1st person narrative type RPG. Voice over would work in a 3rd person narrative type RPG like Witcher or Mass Effect but not in the elder scrolls.
How does view perspective change how VA affects gameplay?
You know what might make it more immersive? if you could pick what you say by... SAYING IT! How's that for immersion? you hear yourself speak the words and the game responds. Too bad they are neither including that into the Kinect patch upgrade nor would I be able to use it if it did.
I hate kinect and refuse to support it (360 gamer)

There are software voice recognition solutions out there though that they could take any mic input and parse it through to add this (and dragon shouts as well) to ALL platforms. I was upset when I found out ME3 was adding voice support for kinect only and now this. FFS GTFO of here with your greedy exclusive BS Micro$oft and stop trying to shove your worthless pos accessories down my throat. Voice recognition has been around for YEARS and now suddenly M$ has got exclusive rights to it? WTF?!?
I understand why.... it's easier and cheaper on the developers to use kinect as it handles the voice to text itself with no cost to the developer (licensing those voice recognition programs can be pricey) but cmon... Look at the kinect's target audience and look at YOUR target audience and just how much use will it really get? Not to mention limiting yourself to 1 of 3 platforms. The only legitimate reason I see is the kinect offloads the processing of voice translation so they don't need to share CPU power with it.
But I digress. IMO lacking the speak to answer option I think that having VA would make the story telling more immersive, however due to the sheer # of choices you have in character development, it would either be too generic, or take way too long (understatement of the year right there) to record and process all the dialogue.