I came across somebody building a microcontroller project with sensors and serial communication. He was prototyping his project using Arduino but the final production system would be a PIC. As far as I can tell PIC and AVR libraries and code won't compile on each other. Code written for an AVR processor won't work on a PIC without some modifications.
I'm wondering why he would rewrite everything to work on a PIC rather than prototype with an arduino, and then use the same code to program the corresponding AVR chip that was programmed in arduino. As far as I can tell arduino libraries are supported by AVR development tools like atmel studio. It doesn't make sense to me.
Is there something I'm missing here? Are there limitations with using arduino for prototyping and using the AVR chip inside the arduino for production that I am not aware of?