The difference between the game back then to now is that then, you only heard voices when you spoke with someone or when you were listening on something that has a cutscene or something.
Now the game is more about eavesdropping and learning things on your own. Almost everyone talks and you have to sort out which conversations are important or which are not important. I can bet that that there is more dialogue in this hitman than there is in the first 4 games combined.
So considering how much dialogue there is in the game, I can see why they decided to go this route.
I believe torben said this back when Colorado was being first previewed on a stage with him and Travis.
At least every most unique npc, ET and story Target have different voices and to me, that's all that matters.