For some people and uses, yes, you are incorrect. Word documents may not render correctly or at all if the user doesn’t have the right version installed. Footnotes and other semi-complex formatting can be especially problematic and you can’t guarantee that people will see what you want them to see unless you force them to have a narrow range of versions.
PDF’s tend to solve this problem because they are essentially just images of pages that, in theory, look the same no matter what type of system you view it on. All it takes is a PDF reader to ensure that they see what you want them to see. PDF also has better security in case you don’t want people to just grab your ‘examples’, edit them a little and turn them in as their own. It certainly isn’t a perfect or even a great format either but it does have some advantages over Word documents for some uses like this.