[atduskgreg]

Dead on. Also, the main point when you're getting started with physical computing is not the processor, but the actual hardware you can plug into it, the LEDs, buttons, motors, thermistors, etc. One of the Arduino's really big advantages for beginners is that it is relatively "transparent" in terms of cognitive, cost, and setup overhead in this regard. It gets you to actually plugging things into it and seeing them blink the fastest and cheapest by an order of magnitude.