I know the reason we were so insistent while I was still there was because Quark 4 couldn't read anything newer than Word 6. That's not an issue anymore, so I suspect this restriction is legacy code no one ever checked. A couple of freelancers might have such old systems that they don't have a newer version of Word, but I'd be surprised if it's more than one or two. Most folks upgrade their systems at least once a decade, right?

Good luck.