Why not just post the CD-ROM online so customers can download it?
Not everyone is on a high-speed connection (particularly people in less developed regions), so this would discriminate against people on dialup. In addition, putting up a separate area with for-pay content would be redundant because it would largely duplicate the existing site. Thirdly, it would also go against the basic premise of this site, which is to provide free, anonymous, access to these texts. I don’t want to end up with a two-tier site, one which only wealthy first-worlders with credit cards can access, and a ‘ghetto’ for everyone else. The whole point of the CD-ROM is to support equal access to this content, not lock it up for rich people.