Well, you're probably just used to the Warcraft 3 voice acting. I also am not a fan of SOME heroes from dota 2, but I know why's that : The immersion factor of the old Warcraft 3 game can leave marks on how you want things to sound like. Dota 2 is taking a step towards being different from the style of the wacraft 3 one, and it's doing mostly good.
You'll get used to it. If not, meh. Mute them ;D Or wait for the option to mod them, if it will ever be available.