Amex has been pulling back on credit across the board. They've been getting burnt on all the credit they were dolling out over the past couple years and are trying to get back to servicing customers who pay their bills every month. I know when I picked up my business Amex cards two years ago they gave me way more credit than was probably justified on a business case at the time. They haven't touched my limit yet, but I also pay them off every month, which is Amex's stated 'ideal' customer.
Hell, Amex cards you could carry a balance on at all are a fairly recent introduction.