oh, i'm sure they exist. there's no reason why a printer can't run linux. It's just that when most high end printers got UIs (mid to late 90s), Windows was the only decent dependable, supplier-backed option available, really. And since then the software evolved and thus stayed Windows-specific.
Similar reasons for why most other industrial / high-end professional devices run Windows. Effectively, Microsoft has locked in an entire industry (and as long as their developer support keeps kicking ass, few in the industry mind this).
Hmm. Most of the multifunction, networked printers I've had to deal with in small business offices run NetBSD. In fact, I don't think I've ever seen one that runs Windows. Of course, my experience is limited to only ~9 offices, but I just assumed they were all like that.
Similar reasons for why most other industrial / high-end professional devices run Windows. Effectively, Microsoft has locked in an entire industry (and as long as their developer support keeps kicking ass, few in the industry mind this).