Yes, it's not unlike serial communications capabilities. The standard AVR chip used in an Arduino (168/328) has internal USART hardware circuitry that is attached to only pins 0 and 1. However one can use software functions to do serial communications on any of the digital I/O pins. So it's a case that every specific AVR processor type used has built in hardware capabilities that are assigned to specific I/O pins. The AVR datasheet for a specific processor is the best source to understand the 'extra' capabilities of each and every I/O pin.
Lefty