The levy in fact guarantees artists an income that is proportionate to their success. These amounts are distributed based on the number of sales made by the artists and also based on the broadcasting of that music.
Of course, an artist who manages to create a very popular product will earn more money from the royalty than someone who creates a product that isn't popular.
This works the same way for inventions. If an invention is very popular, it earns more money. If it is an invention that isn't very popular, then there will be less money.