Google tells me that the AMA made about 468 million last year in revenue. If they made that much from the codes it seems like they wouldn't necessarily pass the IRS Public Support test. (Unless somehow this licensing counts as "public support."

I seem to remember this test is why the Mozilla Foundation and the Mozilla Corporation exist, but I could be mistaken.

Edit: Seems that the AMA is a 501c6, which is a different kind of non profit.