I would also point out your natural pure platinum crystal has dimensions of .6 cm by .6 cm by .4 cm.
That's not an ore deposit, it's a pebble.
These arguments for platinum are getting increasingly ridiculous. The best arguments that have been offered reduce down to "D&D did it, so it's totally realistic," "It's already in the game, so you can't take something out of the game once it's already in (nevermind the broken economy, half-implemented mountainhomes and dark fortresses, the cave-in system, underground rivers, chasms, guild masters, or some other things I can't think of at the moment, when something goes into DF, it never comes out)," "it's better to have metals that don't do anything than it is to have metals that can be used for something," and now, "if you remove platinum, you have to remove dwarves, because they're unrealistic".
Toady just put in the real values for densities, as best Uristocrat could research them, for the real materials that are in the game because the real materials are treated realistically. Toady also put in real animals as faithfully as he could given his time constraints when they were the donation drive winners. Toady also put in Peach Faced Lovebird-Men, because in his fantasy world, anthropomorphic animal-men exist as a fantasy element.
Toady treats the real things seriously and as realistically as possible not in spite of the fantasy elements, but because adding realism into the game makes the whole game feel more real and relatable, even when they involve dwarves swinging candy axes at a vicious marauding Peach Faced Lovebird Man.