Why do Arduinos ship w/ 16MHz crystal instead of 20MHz?

Question

Why do Arduino boards ship w/ 16MHz crystal instead of 20MHz? They are spec'ed for operating at 20MHz, after all.

I guess there are a few advantages to running more slowly (lower power consumption, longer life), but I must be missing something.

Answer 1

I'd buy into the answer on the Arduino Forum:

The original ATmega8 Arduino ran at 16MHz, which was the top rated clock speed for the ATmega8 cpu used. When "upgraded" to ATmega168 (with a 20MHz top cpu speed), the clock was left at 16MHz (probably) because the designers thought that more people/code would have backward compatibility issues with a new clock rate than would benefit from the extra 25% cpu performance. I certainly think they were right...