Most of the components are a step down from top of the line. The cost difference between top of the line and a step or two down is upwards of an order of magnitude. Really. The 8GB flash chip in DX50 goes for around $4.50; the 64GB flash chip in DX100 goes for around $40.00. DX100's Sabre DAC lists at $65; DX50's Wolfson DAC is about $12.50. DX100 has a substantially larger display, an optical output jack, full working Android support (not sure if there's a license fee for that). All of these things add up.
Yes but iRiver charges 3 times the price. They both use the same screen, they use the 8740 sac, the component cost is about the same as I have worked on the AK100 and there is nothing special in there. It is the implementation that iBasso did with the DX50 that makes it special. I can hear the differences all the more between the AK100 and DX50 with my TH900. I enjoy the iRiver but the DX50 to me, just has better implementation for 1/3 the price. I would not call the 8740 a lesser dac chip, just one that renders differently with some preferring the Sabre chip and some the Wolfson. Cost and specs are not everything. It is all good.