I just came across a recent mailing from AMEX that lists the Platinum Card benefits and services. Doesn't sound like you have to have spent any money on the card:

here's the wording:

Premium Global Assist Hotline:
Whenever you travel more than 100 miles from home, you have emergency assistance, including emergency medical evacuation to a medical facility nearest to the card member's home when determined necessary by a Premium Global Assist physician.

then there is a footnote:

The Premium Global Assist Hotline must arrange all medical and visitor transportation. Because the Premium Global Asisst Hotline is an assistance service, we cannot reimburse you for expenses you incur on your own.