For documents that attempt to provide ethical or legalistic guidelines it is a very serious matter. Imprecise language or language that leaves too much room for interpretive 'wiggle' is truly a problem.

The OSD isn't a legal document. It's a community-supported guideline. It is based on the Debian Free Software Guidelines, which isn't a legal document, either. It isn't intended to hold up in court, because it doesn't have to. This works because the OSI owns the trademark for the term "Open Source" and gives rights to use the term only to licenses that comply with the OSD. If a company wanted to contend in court that their license qualifies as Open Source when the OSI says it isn't, then a judge would likely say that the OSI owns the trademark and can stop (or allow) whomever they want from using it under trademark law.

Note that the OSD and GNU Free Software guidlines are actually quite similar (both ESR and RMS have stated this in the past), but the OSI is looser with its interpretation.

The software can be used in the most general, non-technical sense . . . contrasting interpretation . . . The software, if it is compliant with the OSD, must be free of license restrictions which forbid its inclusion in a commercial product . . . These two definitions are really greatly at odds.

I don't see how they are at odds. Rather, they are complementary. The OSI considers "use" as both the running of binaries and working with the source code (using it as part of another program or modifying an existing one). It could also mean linking (dynamically or statically) to a library.

So when the OSI says you can't stop commercial software from using Open Source software, they refer to both commerical end-users (those running binaries) and the inclusion of the source code by commerical developers.