Polishes don't protect paint, they remove it in varying levels and restore the finish. It is wax and sealant that protects the paint. I've had 3 red cars and only had a problem with one - a 1987 Rover 216 and that was never waxed. SRP always brought the colour back though but didn't protect it.
Older cars which only had base and top coat with no clear are more susceptible to fading, in fact if they aren't waxed they will definitely fail.
New cars with clearcoats almost never fade (its not impossible.) The pinkish looking modern cars you'll find are generally like that because of the poor way they have been washed - it is swirling in the clearcoat that affects the optical clarity of the finish and make it look pink - same issue as black cars looking grey.