it didn't even "have" to land in austtria, they landed there because it was easy. They probably had fuel enough to land in any one of a ton of other countries if they so chose.
No, they certainly didn't have to land in Austria. But somehow, god knows why, certain countries closed their airspace for that specific plane. I'm inclined to belive that more countries would suddenly close their airspace too if plane chose not to land in Austria but to go to some country where Snowden won't be in danger of being arrested - France, Spain, Portugal and Italy are hardly the only one that would bow under US pressure.