Big companies, yes. Small businesses, not so much.

There's certainly an unrealized support cost. But in my experience, it's pretty common to see several different manufacturers and OSs across a small business. When they need a new laptop, they're either picking up what's cheap at Best Buy or handing down machines when the boss gets a new one.

Unless their Windows image is based on the out-of-the-box OEM install.

I would imagine that any company imaging their hardware has their own custom image to coincide with their windows licensing agreement and not on whatever was on the first box.

Yeah, that doesn't happen.