This is chosen by the companies itself. They do get some revenue for the cell phone chargers. So, any third party company could produce a cell phone charger which is capable of charging wide array of cell phones. The good thing is that the companies mostly 'group' their models so they could be charged by a same charger model. Recently I bought a charger (both AC and DC that could be used at home or in a car's power outlet). This is a very good utility for the frequent flyers.