I am not sure complaints are related. I am upgraded every other flight and I have never placed any complaint so far (why should I?). Moreover, when travelling with my partner they always upgrade the two of us (my partner being only 'bleu'). But I am quite sure their computer system indicate some rating codes adding to the status. Afterall, it would be quite normal to reward a bit better a customer who buys its own tickets (rather than his company), who uses AmEx as a flexible friend, hires partner vehicles, sleeps in partner hotels, etc, etc... That's the essence of those loyalty programs I believe!