You have no idea what you are talking about rcook. While some of the actual pigments might be the same, the carriers, and processes are totally different. Why is power coat so much more durable than paint? Its not because it is a thicker coating...
Now - decals adhering well to power coatings does depend greatly on the formulation of the RESIN base of the powder. There are literally thousands of powder formulations for different applications, durability, etc. The resin base of some have properties that ultimately make the finish less receptive to regular adhesive vinyl. Different resin bases ranging from urathanes to nylon, etc along with different additives to aid lubricity, etc are also present. While the end result of many powder coat finishes might look the same as the same color traditional paint finish the actual makeup of the coatings in the end really have almost nothing in common other than the color.
From Linetec regarding powder coatings.....
"The primary component of powder coat is referred to as the resin. The type of powder coat system comes from the resin system. The powder coating formulation is much like a liquid coating except that most of the components are in solid, melt processable form. The exact composition of a particular powder coating is often complex and proprietary. In general most powder paints contain resins, pigments, fillers and additives.
Resin System: Resins are the key component of powder coatings. The range of powder coat resins used have increased to meet the demands the architectural market sector. Resin systems include: Kynar (PVDF), Polyester, Super Durable Polyesters, Urethane, Epoxy, Acrylic, and Nylon.
Pigment: Pigments are the material added to the paint to give it color or to enhance certain physical properties of the coating. The selection of pigments is done on the basis of physical needs, durability, gloss, color fastness and chemical exposure. Pigments are both naturally occurring as well as synthetic. Typically solid particulate materials such as titanium dioxide or carbon black.
Fillers: Used to reduce cost of the coating formulation and to improve specific properties such as flow, surface texture, lubricity, etc. Common fillers include barytes, calcite, mica, talc, whiting and wollastonite.
The raw powder coatings, composed of resin, pigment, curing agent and fillers are mixed dry and then melt mixed and extruded. once cooled, the mixture is chipped and ground into finely divided particles. The chips are ground to a very specific particle size distribution depending on the application.
The particle size is important to the performance and appearance of the coating. The size of the powder particle can have an influence on the behavior of the material in the painting process and the final film characteristics."