I think the poster was saying that the machine was rejecting the mag stripe cards. Either it didn't have anything but an EMV reader or was configured to reject swipe transactions. Almost all credit cards have a PIN for cash advance transactions, but as reclusive46 said most consumers without a chip-and-PIN card don't know their card's PIN.

With a chip-and-PIN card, the PIN is stored on the EMV chip. With a chip-and-signature card, the cash advance PIN is stored with the card issuer. This is why some unmanned kiosks that only accept EMV cards still work with a chip-and-signature card. If the transaction requires authentication and kiosk does online transactions and compares the PIN you enter with your bank, the transaction will go through. If authentication is required and the kiosk does offline transactions which would attempt to compare the entered PIN with that on your card - and in the case of a chip-and-signature card there is no PIN stored on the EMV - the transaction will fail.

There are few chip-and-PIN cards available in the US currently and none are AmEx. Even those that are chip-and-PIN tend to give a preference to signature verification. While these cards will work in unmanned kiosks that do offline PIN verification, the preference for signature verification might lead to a few merchants refusing the sale. (There have been reports of merchants who refuse anything but chip-and-PIN transactions.)

It's hard to say which direction things will go after EMV becomes more widely accepted in the US. Visa has indicated a preference for signature transactions. MasterCard prefers PIN transactions. I personally prefer PIN-based transactions - no paper receipt to sign - and I think merchants do too. Merchants prefer PINs because the consumer has little recourse in the case of a fraudulent PIN transaction. The assumption is that only you know your PIN. While there have been ways to spoof the PIN, it requires the original card and a willing merchant to make it happen. It's a little more involved than scribbling a fake signature.