I agree with you on that. My personal way of handling it would have been to have the policy on the front page of any website, forms or whatever, when purchasing tickets. No way anyone can say they do not know the policy.
If somehow, someway, they get past it (i.e. travel agent or someone else buys the ticket, at check in, the policy would again be in force and the passenger informed.
I don't support a database for passengers, simply because I could see the airline (who have been debating the idea for years) using selective pricing (unrelated to weight, seperate issue) or discriminatory pricing.
The only reason I even have opinions about this, has to do with a recent flying experience, I had a seat, and the row I was in was vacant. In essence I had 3 seats (and was quite happy, got to stretch out, etc). The stewardess was joking that I was getting 3 seats for the price of one, and that one day the airline would figure out a way to recoup that money, because the airline always win.
I was laughing, but it did get me thinking, could the airline make me change seats because I'm getting more then I paid for, or could they try and charge me more, because I am getting 3 seats, for the price of one? And would anyone doubt that this idea hasn't gone through some airlines executives head?
Back to the fatties (and you know who you are). Buy 2 seats or take your own car.