the DOC format is not open
"Not open", here, actually means that it's controlled by Microsoft (who can change it at will) as opposed to decided upon by a committee (such as w3c for html). The format's specs is available for everyone to peek at -- if not by Microsoft, then by people who reverse engineered it.
So why isn't Microsoft (or any such proprietary players) making an issue out of this?
Why should they? They control the de facto standard of word processing documents. Allowing others to read their proprietary formats ensures things stay that way. This leads to more MS-Word sales. It additionally gives them a free hand to change the format whenever it fits them in order to introduce new features. Competition, by contrast, needs to rely on their own formats to add features, rendering their documents unusable except by other users of the same software.