Many people might think you're talking figuratively about paying for every byte. I'll add for others that 8-16-bit MCU's still sell billions of dollars of volume specifically to increase profit per unit by using tinier, cheaper chips. Likewise, stuff like eCos lets you include just the software you need in the RTOS to further shave off ROM or RAM needs. This helps per unit since suppliers often charge extra for extra RAM/ROM on a specific chip. Finally, reliability and security can improve a bit by simply having less software or hardware to screw up.
