I think the "wahhabis" do follow orthodox sunni islam its just that the hanbalis are the most conservative of the 4 schools and that most sunnis follow the hanafi school which is the most liberal. But a certain 'wahhabi' scholar called sheikh albani said that driving a car was much better than riding a donkey
so its permissible and that only covering the hair was needed.
I wouldn't categorise the Wahabbis as the mainstream interpretation of Islam though, but they definitely have a lot of basis for their intepretations and have a lot of influence considering they are but a minority of the Muslim population.
You're right Hanafis are the most liberal and Hanabalis the most conservative but the Wahabbis are a different sect altogether - they are Islamic purists, if you like.
For them the veil is a mandatory part of Islamic tradition since they interpret the application of the Sunn'ah as Muhammad making his wives wear veils.