Manufacturers first priority in designing professional car paint isn't durability. They know auto body guys want to get a good look on as fast (and cheap) as possible. Ease of use and the speed it can be applied are what makes paint sell so a job can be profitable. The car is not likely to be in the owner's possession long enough for him to come back and complain. Bike paint jobs (as mentioned) take a greater beating and require the most durable kinds. In my experience, a base coat/clear coat system (when the color coats are very thin and need to be protected by clear top coats) are not as durable as a polyurethane enamel like Dupont Imron (although I use both).
There are all sorts of factors that contribute to paint problems once the best ones have been selected (and the worst ones avoided). Of critical importance is the amount of time that has elapsed between coat applications (which very depending on temperature and humidity). And of course you have to usually pick reducers that are matched to the temperature when spraying (and one can't spray when it is too cold). If too much time has gone by the top coat won't bond with what is underneath. The best show quality paint jobs require lots of sanding between primers and color coats and clears. This can lead to contamination that keeps later coats from sticking as well. I use cleaners that paint companies design for this purpose.
Over the years I've discovered what types of paint are the most durable for each layer (primer, clear coat, etc.) and will sometimes intermix products from different companies to get the best results. I also often use a sealer paint between the primer and the color. This increased the bond between the two and provides an even undercoat color for greater top coat consistency and clarity.
And by the way - as has already been said - baking a frame does not increase its durability. The general description of painting steps I hand out to my framebuilding class students is one full page but the instruction sheets for my painting class students are pages long. Of the 3 primary skills used in making a frame, brazing, filing and painting, I think painting is the most difficult.