Although the “radio test” is cute, it doesn’t really apply to searches in 2010 and beyond. The media that more than 90% of all traffic is derived from IS NOT the telephone, so having to spell your domain name doesn’t really apply anymore.

Dashes/hyphens in the domain name IS a better strategy…

The same reasons you give for hyphens/dashes in your file names apply to domain names as well. Using hyphens/dashes will help Google understand the name of your domain easier (just like your file names) and allow the algorithm used by its spiders to gain a better sense of what the page is about.

An even better strategy? Spend an extra $10 and grab BOTH versions…
http://www.thisisabetterdomainname.com and http://www.this-is-a-better-domain-name.com.

@Jamie – go grab that hyphenated domain name!