The AA and RAC sites and guides mention it too as does any guide book to Austria which you'd surely look at if you were so new you didn't know any locals or German.
If you weren't going to Austria - merely passing through? Probably - not surely.
Driving into Central London you see the "C" sign, driving into Austria you see the Vignette Symbol with afaik, "toll obligtory" which is in errrrrrm English. It's not a "german Geist" to have a igh toll, its to screw the Germans which Austrian coppers luv doing.
We can keep this little argument going all day - but my point is simply that it [it] does [/it] happen that people actually are ignorant about it, and that 400 Euro is excessive unless a person knew about it and decided to risk it. The fine in London is 100 pounds, which is reduced to 50 pounds upon prompt payment. A little more reasonable don't you think?
If you think 400 Euro is ok - then how about 2000 Euro? Is that ok too? If you extrapolate this in the extreme - I remember a Star-trek episode where they visited a planet which had the death penalty for even the slightest misdemeanors. Worked fine since everybody knew about it. Except for the "tourists"
If the Austrians were interested in a fairer system couldn't they simply put up toll-booths (with chip-lanes so the regulars wouldn't have to queue) which would eliminate any such incidents. I reckon they're raking it in and see no reason to change their ways...