I was also annoyed by this error, which from what I researched is not due to Maven itself, but to a way that M2Eclipse implementers found to resolve certain dependency-related issues on previous versions.
It probably needs to be fixed by someone more directly involved with the “Mavenization” of the openHAB code, at least because Eclipse is the recommended IDE (and M2Eclipse is what comes with it). In the meantime, using the Quick fix solution to ignore the error should be good enough as apparently Karaf is not needed to run openHAB from Eclipse.