The problem with the search engine optimization argument is that I can't say I've met that many people who are actually able to get good rankings, and then you have a problem of trying to monetize any traffic that you do get, what do you sell to kids looking for information about tv shows?
And even then when people have domains with high search engine traffic its often not seen as adding a whole lot of value to the domain since retaining a high ranking requires constant work as compared to direct type ins. Its easy to say a domain would be worth more if developed but tha fact is development takes times and money, and in many cases lots of equally good domains are available right now.
I think goh is suggesting that any value would be in the website created, as a result of the time spent creating and marketing a site rather than the domain in itself having inherant value.