Ya I don't carry my card, it's never been a problem IAH included. But my BP has always said *Gold, that said I'm also quick to offer my AP number when in doubt.
PTY always asks for my card, to which I respond simply with the number and what program I'm in, get's the job done. I might start carrying it internationally a bit more now, but to this point I've never needed it, I do have a pic on my phone, but obviously they can't swipe that.