In years past, the effects of oxidation were far more obvious as it would break down the binders in the paint, causing it to look matte and powdery. You may well have seen old post office vans where the paintwork has turned pink, and you might even see what look like white patches of dust. This was why T-Cut was such a popular product, as it would cut away all this dead paint.
On modern cars the effect is far less obvious and may only be a very slight hazing to the surface of the paint. It really is just the very uppermost layer of the clear coat which is effected so is very easy to remove with a light polish, it can even be done by hand.