Having made this bold claim, have you ever actually tried to run a natted eyeball network? The last two natted eyeball networks I worked with could never figure out which aspect of NAT hurt more: the technical side or the business side.
My small telco-owned ISP NATs all of its DSL users, but you can get your own IP on request. They have about 5000 users and I think they said I was the eighth to ask for a private IP. I have to say that it took several months to realize I was behind a NAT, and that only because "my" IP showed up in the CBL blacklist of botted machines, and after great household excitement trying to deworm all the laptops, I poked around in the router and noticed that the other end of the hop to the DSLAM was numbered in 172.16. space, and it turned out the botted machine was one of my neighbors sharing the IP. Based on that experience I'd say that there is some cost to putting your consumer customers behind a NAT, but probably not as much cost as buying IP space on the rapidly developing open market. R's, John