They dont actually have Austrian accents(Austrian sounds more German) or talk like Arnold, they actually talk like Ranier Wolfcastle in the Simpsons, I know a lot of people think the accents are "similair", but they are very different, I dont even know if the accent from Wolfcastle/Skyrim exists in real life, I've only heard it as a fictional accent.
If the voice is (purposeful or not) an imitation of Rainier Wolfcastle, and Rainer Wolfcastle is an imitation of Arnold Schwarzenegger, aren't you just arguing semantics?
It's considered "Austrian" by the majority fanbase since Arnold (and thus Rainier, the satiric take on Arnolrd) is Austrian/American. It's just a stereotype that stuck because it's comical and everyone loves the Governator.