Actually, the best armor types in video games metal wise (assuming they don't use mythril or oricalchum instead) tend to be platinum every bit as often as gold. ...which is an even softer metal, but eh. :V
Yeah, that can often be true, but, as you say, the same principle applies (conflating value with utility).
Really, in the case of a lot of those games, it's not really like that for a practical reason so much as a convenient shorthand for, "this here sword's even better than that there sword if yer too lazy to look at the stats!" I don't think it happens as often now, and if anything, likely any gold or platinum sword is either just plated with those metals or like Goldie's armor are enchanted to the brim.
Old fashioned RPGs aren't the best reference for that, in other words. 
Well, yes, I know. My point is that the rules of the universe in question trump physics (as much as I hate to say that).
Though in the case of Persona 3? I don't remember there being anything about gem swords like that. Granted, I haven't gotten far into the game, but I would think that even though this is a game where high school kids summon powerful spirits via doing something that suspiciously looks like shooting themselves in the head, that there would be slightly more realism with the weapons at least, material-wise. So there's that to consider. ...People who have gotten further into Persona 3 can correct me on that though. ^^"
Well, I dunno, but I'd guess that there is some mechanic as to why the sword works (firstly, magic, secondly it is probably not literally just made of gemstones).
It is made out of jewels, but they are also jewels from the crown of an angel so that makes it speshul.
Yeah, something that magical isn't really expected to follow real-life physics....
The description also states that it surpasses Excalibur, but P3's Excalibur doesnt shoot beamus and it isn't made of humanity's hopes and dreams either.
Yeah, I'd agree with this. "Surpasses Excalibur in the Personaverse" isn't the same as "is stronger than Saber's Excalibur".
