I recently bought a WiFi adapter for my Raspberry Pi for about 8 USD. At the same time, WiFi modules for Arduino and similar microcontroller boards cost several times as much.
What is fundamentally different between a USB WiFi module and one sold as a peripheral to micocontrollers? Is it just the economics of high-volume/low-cost, or something fundamentally different in the hardware?
(I've heard about the TI CC3000 WiFi chip that is supposed to be under $10, but I haven't found any place that sells just the chip.)