.. they changed some of the voice actors from the trailer version? http://www.youtube.com/watch?feature=player_detailpage&v=oSL-r9AIEEU#t=299s

For example Alvor sounds way different in the gameplay trailer than in the actual game? Also the woman screaming about a dragon sounds different aswell?

I dont know if this has been discussed here before but I do find it weird that they changed those voice actors.

Because they needed better voice actors, it's Skyrim, the hardcoe Land of the Nords, they changed the voices because it sounds better and it's more believable

I'm guessing that a lot of the voiceovers we heard were placeholders. The game wasn't finished yet, and they needed to make a demo.

imo the alvor from the demo sounds way better

This...
... and a placeholder might be one of the devs filling in, but VA requires not just good sounding voices, but professionals who don't waste time and money in the studio. It. ain't as easy as it sounds.