Good lord this thread went full retard. And you never never go full retard.
I love the crap about receiving a fax or an email. What do you think that document will look like printed on some doofuses ten year old inkjet at home that leaves streaks down the center and blobs of wrong colored ink? Because I'm sure someone is flying with something that looks like that in their wallet.
Shoot a picture of the damned thing and make a PDF out of it with your phone and upload it to Dropbox or other cloud location. Then stuff the original in your wallet. You have the PDF on every freaking device you own from then on if you need it, and the other one will be there in your wallet until it's time to renew anyway. If it was printed on a laser it'll imprint half of itself onto the other side of the paper with the warmth of your butt cheeks over the years and you'll never even notice anyway.
I agree on "full retard" when one starts talking about asking for a Chief Counsel opinion on a pretty "who really cares?" issue.
But to be a bit technical, the fax replacement fromthe FAA is temporary:
You must include a check or money order for $2.00 made payable to the FAA. The Aerospace Medical Certification Division can fax you a record of your certificate that is valid for no more than 60 days, which should be enough time to receive your replacement certificate. To receive this fax and order a duplicate certificate, call (405) 954-7674 to reach the duplicate certificate desk. (my emphasis)
So it is actually not a copy of your medical, but a temporary record that you have one.
I think the difference between "official" and a copy, fax, scan or whatever isn't where it comes from but the existence of a pen-and-ink signature or other official marking of authenticity, which still means something in certain quarters. The quality of duplication techniques just means difficulty in telling a duplicate from an original, but both the US and most states have laws about counterfeiting (which doesn't just apply to money).
I haven't received a replacement of a lost medical, but I did receive a replacement medical some years ago due to a Special Issuance. Those replacements bore original signatures. I suspect the ones sent within 60 days after the fax do as well.
The bottom line is that, unless you were doing something incredibly stupid, the issue would not even come up. There's no identification function to a medical certificate and, as a number have pointed out, an FAA Inspector can simply look up for qualifications. But if compliance with a few rules isn't anathema, I'd say the requirement to carry a medical on one's person means the "real" one - bearing pen-and-ink signature, just like the drivers' license you are required to have on you isn't one you made using a color copier and laminated.