I am an embedded system designer, mainly use Microchip PICs and ATMEL AVR's to build industrial control systems on a daily basis.
BTW, Microchip tried to buy ATMEL not long ago (it didn't work) and it's a bigger company with more support and production. Older companies (Texas Instruments, Motorola, INTEL, ...etc) were more famous when microcontrollers started in the 1980's and 1990's.
All microprocessor/microcontroller chips are made with a couple of technologies in one of a few architectures (no company wants to re-invent the wheel) and those things don't affect anything about the final product (they are simply names and it'd all about what the designer is used to and they all have different packages and capabilities and high-level compilers).
Recently, I started designing PCB's that have an arduino-like header in the center to hold an arduino nano or some similar clone board that get's inserted just like a DIL IC in an IC base, much more reliable longer pin contact though. The boards may contain other IC's or discrete components, relays, ...etc, but most MC IO pins connect to outside professional MOLEX type click/fasten connectors () through opto-couplers.
Small arduino boards, for me, are just another microcontroller chip (that come with pre-installed bootloader and a free, simple development environment) that help me avoid SMD work and that come with nice libraries in their development environment for any "slow" man-machine interface application that are (if the whole system is designed right HW/SW) supposed to last forever.
BTW, I buy my little arduino clones from Chinese manufacturers and they are top-notch PCBs. I have used them, with good packaging) in industrial environments and made complicated C code for PID control and sometimes modified the assembly code to mess with timers and interrupts. I would love to hear other users get the most out of these "products" like I did and not to focus on making "cool" gadgets because there is so much more potential.
That sounds very close to using a PLC and some ladder logic like Allen-Bradly's RSlogix but that is much smaller and cheaper.
I remember when car manufacturers (especially Chrysler) started including a car computer or ECM module in their cars to control emission and injection and stuff like that, that they used to cover the computer PCB with a very thick layer of a very hard funny material that you don't even get to see the components and it was almost impossible to diagnose faults on a component level. Modern PLC PCB's are not much better than arduino PCB's (they are only, probably, covered with an additional transparent layer of insulation that is hard to see). It's like the industry standards now that PCB's for production are very reliable, especially if they are put in reliable cases and electrical and mechanical isolation. I would love to see comments about my experience.