If a non-blogging FTer did it, we'd all have done it by now--especially the SPG since they're so hard to earn in large numbers. Seems like a way to cash in on the referrals, as you said. If you play this game long enough, you'll get lucky and catch a system glitch once in a while (I've gotten a sign up bonus twice on the same card, for instance), but that's too many times for me to believe it without some proof.