Enamel is what we call "shoot-n-scoot" paint. It's cheap and easy. I think your shop got the concept backwards, as enamel is the paint that tends to look good for about 5 years and then fade quickly.
Enamel gets its gloss from the resins in the paint rising to the surface during the drying process. This formed resin layer is actually very thin. If the enamel is sanded or rubbed, or if it erodes from normal use, this resin layer goes away, leaving a dull-appearing paint that can be made to look good temporarily by rubbing it. Go look at one of those faded green John Deere tractors sitting in a field sometime: That's enamel.
Some enamels can be modified with a Urethane catalyst (for example PPG Delstar). This greatly improves the characteristics of the enamel, making it behave much like a urethane. When this is done, the enamel can be "color sanded" and rubbed out, and it will retain its gloss. This makes a very durable finish. I use this type of paint for engine paint...
A significant step above the enamel paint job, which also know as "single stage" paint, is the basecoat-clearcoat system. This is known as two-stage. This system applies a base color that is heavy in pigment but containing no resins, and then a catalyzed urethane clearcoat is applied over the base. This produces an incredible depth, gloss, and durability. This clear coat can be color sanded and rubbed out to produce a mirror-like finish. Most of the show-quality jobs you see, and most new cars, use the 2-stage systems with the urethane clearcoat.
All of the major paint manufacturers offer both enamel systems and BC/CC systems. We've been using the 2-stage systems at my restoration shop for the past 20 years, and it's tough to find anything better. Rarely do we ever use enamel, and never on a high-end car.