Although you ask people to place anchor text in the outbound link, its is estmated that 60 to 70% will use the actual domain url rather than anchor text.
ie. h t t p : / / w w w......
Therefore if I use a domain name not associated with my main keywords I am eliminating up to 60 or 70% of the anchor text that I could have received which is literally
SEO sucicide as linking is costly and time consuming.
For actual deeper page urls, people are more likely to use anchor text due to the length of the url and fitting in with written content on the page or overall site design, etc.
It is really common sense to name the pages around the content which is being written.
Cheers, Chris.