Why use int instead of byte for pin numbers?

And why cripple it with an Atmel chip anyway? That was a bad idea from the outset

Wow! A sudden outbreak of 20:20 hindsight.

Except, the hindsight needs a little focus.

Back in 2005, which useful cheap microcontroller families were supported by free, un-hobbled compilers?
Hint: it's a very short list.