Yeah, interesting contribution André, I have read at http://en.wikipedia.org/wiki/USB_flash_drive and it seems that pen drive/thumb drive were trade-marked by the companies that made it (at the very beggining), and with time they have turned into a word with meaning in itself (synonym with flash drive).  Just like "bombril" is with "palha de aço/lã de aço" and "gilete" is with "lâmina de barbear" in Brazil.

     Interesting like people use creativity in language!

     PP.