That would of had more effect 60 days ago, but a good question.

Sigh. I argue with the love of my life about this all the time.

She's convinced "pure as the driven snow" should be an insult using reasoning exactly like yours.

Unfortunately for you, she (and you) are both mistaken.

This cliche actually pre-dates the existence of automobiles.

"Driven" in this context does not mean "driven on." It means wind blown.

Unfortunately for me, her use of the term is likely to become the accepted meaning of the phrase within my lifetime.

actually, i had always taken the term to be a slam on someone's purity.
i.e. Anna Nicole Smith is pure as driven snow.

I had always thought it originated during the times which snow was "driven" through the smoke, soot and horse hooves of the environment, rather than the "pure" flakes that you caught with your tongue as a child.

Not to mention that snow (even pre-Industrial-era) snow was anything but pure. After all, snow (and rain/sleet/hail/clouds) requires a fleck of dirt to create the water droplet.