In IT, it's a very easy concept. Process control and industrial control systems is another matter entirely. They don't have a firewall team, or an IT staff, or a network admin, or a Windows Domain Architect, or any of that stuff. They don't have 4 days to wait for a change control board to approve access, because they usually need the vendor to fix crap immediately, or lose a few hundred thousand dollars in lost product.
They have Steve, who has been at the plant since God stopped by for tacos. Steve knows some stuff about computers, like how to google common problems, or he asks his 12 year old kid how to fix it.
Culture is entirely different, the level of experience required with IT equipment is minimal in the operation. Most of the equipment comes preconfigured, doesn't change for 5 years, and if it breaks they get a replacement in the mail. And, they are usually required to NOT change network configs, mainly because they can royally screw something up (and generally do).
I'm not making excuses here, I think good change management would be important. But, these guys operate at the same basic IT level as a McDonalds. I wish I could communicate the exact depth and width of the gap between IT and IndustrialControl, but nobody in IT ever believes me.
~Sticky