It's definitely been my policy since the beginning that all companies listed need to mention and link to OpenACS on an easily-accessible page. Basically, within 2-3 minutes of browsing the company's site, people should know that they're using OpenACS in some way or another.
I think we should keep this policy: if pages have changed, we should kindly ask that those who want to remain listed on OpenACS.org continue to mention OpenACS.