Prevent the dough from "oxidizing"?
I'm not a chemist so I'll let wikipedia do it for me:
http://en.wikipedia.org/wiki/Oxidation

As far as it's culinary effects in crusts- I have seen unreliable reference to the flour oxidizing and developing a off color.

I have never seen this personally and I am skeptical of it. Pie crusts can be made just fine without vinegar. Vinegar does significantly tenderize the crust as well as add an interesting flavor.