You can sort-of do analog input-output via the audio ports on the pi, right?

Cool, didn't know that.

Seems like the hardware has to be modified and it only supports 0-1V though: http://raspberrypi.stackexchange.com/questions/8757/using-pi...

PWM is useful because that can be used to drive servo motors and brushless DC motor controllers and other gadgets. It can't be easily replaced with analog output, e.g. from audio ports. OTOH, audio ports are a lot more useful if you need actual analog output.

PWM could be done with an op amp, a triangle wave generator, and a handful of discrete components. It's how the front-end of a Class D amp works. Would definitely be more of a pain in the butt than having pwm ports directly, though.