While Audi pioneered AWD, you can get the same thing from Subaru and Mitsubishi, at much lower prices and with much better performance.
But Audi definitely has a better "feel" to it. Classier interiors, solid build quality... though I thought the A4 1.6 they opened with in the late 90's was a laughable value at the price... One and a half million for a car no better than an Astra? Please... the BMW 316 was ridiculously expensive, too, but at least it was rear wheel drive.
The new A4s are a little easier to justify the premium for, but they're still only for those who can afford them.
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Audis didn't use to be exclusive cars, but they've been moving upmarket and closer to BMW and Mercedes (who seem to be moving downmarket with the A-class and B-class (now
that's a useless car... Merc money for a mini-MPV? (

))).
The space that Audi used to occupy is now occupied by VW, who also moved upmarket. In fact, VW tried to do this too fast, and completely lost the plot with the VW Phaeton (nice car, but too much money for a "People's car")... now they're re-thinking this strategy... thankfully.