Honestly, the 8 bit AVR controllers seem to be used mainly by hobbyists. I have looked for a list of professional devices that use AVRs but I found no convincing evidence they have serious applications in practice.
Regarding PICs, I have found some credible commercial devices, not related to hobbyists, that use them.
I am not aware of any PLC that makes use of 8 bit AVRs, maybe because the PLC designers do not want to become dependent of a single chip supplier (Atmel). PLCs use ARMs, 8051 or other processors that are produced by many manufacturers.
Also, 8 bit AVR are weak for industrial applications. You could hardly implement a serious modern PLC using AVRs.