To answer the OP's question, yes, US Airways does indeed give out DM membership cards. Or at least they used to, because I got one way back in 2005-2006 when I first opened a FF account with them. Do they still do that, I don't know. But I definitely love to swipe that card at the kiosk when checking in, because that's the only time I ever get to use the card.
Yes, it does have the magnetic strip at the back.
And as for preferred members, the average time taken to get the actual card by mail seems to be 1-2 months. Funnily enough, I received not 1, but 2 Silver preferred cards, with a month's gap between both. Go figure.