Technology has continued to advance, allowing the same devices to be produced at a lower cost - this comes in the form of paying off design investments (such that economics and business needs allow them to lower their gross margin on mature products) as well as improvements in the manufacturing process (improved yields - and in some cases die shrinks) that drive down the prices of the components. This has been going on since the dawn of electronics.
Also, the chinese no-name manufacturers have stepped up their game, such that margins for manufacturing of some simple boards are almost non-existent - notice how you can get a clone pro mini for less than you could buy the components for. I think in these cases the product is being sold at near breakeven - they're just trying to keep the factory humming and the workers employed while hoping for more lucrative jobs (China: The Land of Overcapacity)
Note that that second sort of dirt cheapness vanishes the moment you step away from the ones that the chinese vendors have chosen to make and sell; there are lots of more expensive electronics, it's just the mass market basic stuff that is available for less than the cost (to us mere mortals) of the parts used to make it.