Unless a domain name is extremely simple (i.e. "Plumbers.com", "iPods.com", "dictionary.com", "cancer.com", etc), I cannot believe in basing the valuation on traffic you hope comes from directly typed-in traffic. This just fails the common-sense ROI estimation.
There are a number of cases where a visit to your website will not pass a REFERRER. This makes a lot of people incorrectly assume all of the traffic is from directly typed URLs. So, it's understandable people believe there's a higher value based on that.
Complex multi-word phrases are far, far less likely to be directly typed-in by internet users. Very few people are inclined to type "sanfranciscocardiologist.com", for instance.
HOWEVER, I believe there *is* value in registering those mult-term names for the purposes of SEO keyword optimization. Keywords within the domain name are quite valuable for ranking on MSN Live search, and a bit less valuable though still impactful on Yahoo! and Google.