Just to avoid a misunderstanding: You are not talking about hacking the source of moodle.org to disable the "Rate as useful" drop-down for posts which start a discussion, rather about an amendment to the algorithm of making one a Particularly helpful Moodler, right?
Before going in to details, how is it possible to make a difference beween useful in moodle.org but not counted as a qualification for a PHM? If an OP could be useful, then by posting a useful OP somebody makes himself useful. If an OP can not be useful, then why is there a "Rate as Useful" button in the first place? Apart from the many reasons other have braught, I have two arguments for the usefulness of an OP:
1. An OP need not to be a problem or a question, it could very well be a report, a summary, a write-up solving a problem.
2. A good question is a good thing, as all teachers know (but not allways willing to accept ;).
Now to the "algorithm": One useful rating every 6 months. I don't find it an exciting one, something easily settled with your office-mate, for example, for a cup of coffee every 6 months.
No, seriously. First thing, what is at stake? I have this "badge" for many years and can not think of a single reason why it (the badge) is useful. At first glance one might think of a (military) breast plate. The casual visitor (the commoner) knows that this is an important person. But if one clicks on the badge, he's told, "These people have written a lot of useful posts in the forums recently, as determined by the Moodle community...". Then, if the visitor is that observant, he could get the whole list forum posts by any person. Or, is the badge for the PHM himself, kind of a reminder to be seious? Oops, that shouldn't limit my freesom to crack a joke!
Whatever the use of the badge, it has been there a very long time. As I understand, the current initiative is to _automate_ it. Now that is highly explosive: moodle.org forums are well-known to be polite and helpful. That doesn't come from nothing. That is a culture which was set and nursed by an equally cultivated team of leaders. A personal touch. Now our Community Leadress comes up with this bright idea of lending that to a bot. Sorry, I am not the least inclined to talking to bots, please releave take me out of that group before that happens. Just a passing quesion, aren't you making yourself superflous by automating your job?
P.S. Yet another painful discussion for discussions' sake in the (amalgamated) Moodle community sites form. Now I've spoken, I can forget the topic and spend that time for something Useful (not a typo ;()