Just to clarify something: There is no such thing as "self-plagiarism" just like there's no such thing as "self-escrowing". If you copy/paste or repost something that you, yourself, have written it is by definition not plagiarism. So please, let's stop repeating this meaningless phrase.
Although I'd love to agree with you, my university sees it otherwise, and if I ever want to get my MD, I do have to dance to their tune.
The forum does not come close to having the same requirements to cite sources as is required when writing an academic paper.
However, even if we call it a different thing, the definition would fit just right in this context: "Quoting you own work over and over again in order to get more citations" (or in this case, merits).
He writes content that people clearly find useful. I don't think the amount of merit he receives would be affected by him quoting or citing himself. I think he is probably trying to be helpful to new users.
I might compare your argument to someone saying that I write interesting, and helpful posts in order to get merit, and that the fact my posts are interesting and helpful is somehow a bad thing.