If you look at a lot of major sites they have domain names unrelated to their service.

You just pointed out one... google.com yet its one of the most popular sites on the internet. yahoo.com....another.

deskpro.com, wonderdesk.com, perldesk.com all popular in their field and dont use the keywords you mentioned.

The url is rarely seen. Listings on search engines, script directories etc are all title/description.

Fair enough, not everyone knows what sql means but a large amount do and even if they didn't understand the URL I doubt they'd bypass the site if the searchengine description interested them.

....oh and the most obvious...gossamer-threads.com - meaningless ...so your theory is not quite right.