CR FOLK:
In the 'Vintage Velos' Virtual Museum pictures of Coppi's bike, Alex mentions that the playing-card symbol cutouts on the Bianchi were associated with Bianchi's marketing angle: Pokerissimo -- whichever way you dealt the cards, Coppi and Bianchi were victorious.
A THEORY: is it possible that after Bianchi, the others just, uh, uh, you know, copied? (Coppi-ed?)
Of course, the beauty of these shapes is that they are all fairly compact and fit nicely on lugs, and unlike the triangular braze-windows or drilled holes on some lugs, they are also more overtly decorative.
Brad Stockwell
Palo Alto