No...it's not a questing of oils not being present..more complicated than that...basically the chemical integrity of the paint has been degraded by UV, stress, environment, etc....In simple terms I guess you could say that it has dried out but it is really more of a weakening...the bonds of various components in the paint have been weakened and the paint opens up, more surface area to oxidize. Once the paint has been breached in this manner, applying waxes and polishes temporarily wets the surface making it appear better. The oils and other components do not have the ability to repair the broken bonds....but rather cover up the problem for a short period of time.
Paints, unlike waxes and polishes actually due chemically (catalysis) cure. Once these bonds have broken down...a chalky appearance of oxidation is present. When the damage goes deep...then waxing and polishing can no longer smooth out the surface and new paint is in order.