This is caused in part by not getting the temperature of the paint high enough to form a smooth finish. Metal can withstand significantly higher temperatures than plastic. This is usually why car paints look so much better than Krylon's.
By over-molding their plastic tops around a metal base, Beats was able to increase the tolerable temperature range. Next time you roll into a Best Buy, compare the 'shinyness' and 'smoothness' of the overmolded Beats to any other plastic product made by Samsung, HP, or Sony.
We learnt this through Chinese manufacturing forums where if anything, the idea of 'target demographic' does not apply - Beats simply figured out how to put a nicer finish on their product than the competition using innovative manufacturing techniques and increase margin.