It is clearly stating the definition of a king and the qualification of when DDD is applied. absolutely no diukim ... Just BTW you can come to my house and take my Dayanus certification off the wall after you go to the 2 mara deasras of huge cites (who gave it to me ) and take theirs off too... but first you should go to the person who taught you how to read and understand and verify his credentials
Your diyuk is that the melech case is to the exclusion of all other cases, when in fact that is not the the intention. The Shulchan Aruch Harav speaks in terms of melech because that's the case the gemara, rishonim, and prior poskim speak of (there wasn't much democracy going around then). The important words are הואיל והסכימו עליו, which is a qualification met in every democracy - the citizens agree to the follow the laws of the land. The proof that this was his intention is the source quoted there in רח:
ב"ב דף נה ע"א. מרדכי פ"[ד] דב"ב רמז תקכב. וראה גם תוס' ורשב"ם שם ד"ה אם.
This it that Rashbam, emphasis added:
כל מסיס וארנוניות ומנהגות של משסטי מלכים שרגילים להנהיג במלכותם דינא הוא שכל בני המלכות מקכליס עליהם מרצונם חוקי המלך ומשפטיו
This is exactly what was quoted earlier in this thread with the first link to a source on the matter:
Regarding your comment that people say Dina D'Malchuta does not apply to a democracy, this is not true at least according to the opinion of the Rishonim (Rashbam Bava Batra 54b. Responsa Or Zarua 745) that the king's authority regarding Dina D'Malchuta Dina derives from the consent of the people, which exists even more in a democratic regime. And so rule contemporary Halachic authorities (Tzitz Eliezer 16, 49. Igrot Moshe Choshen Mishpat 1, 88. Mishneh Halachot 14, 119. Yechaveh Da'at 5, 64).
Here's one relevant quote from that Tzitz Eliezer (though it's worth going through the whole tshuva if you really want to learn something on the subject):
ומדברי היש״ש הנ״ל בפ״י דב״ק מתבאר דאמרינן דד״ד גם בזמן שאין מלך והמדינה מונהגת ע״י ממשל שרים וכדומה.