If you look at PartyPoker.com's Overture, one can get a sense of how much marketing $$$$ (lots of tv ads) has been spent to build up that branding.
That's the alternative way to look at things. One can always brand an empty vessel, instead of buying a type-in domain name.....that'll always create an upper-boundary to domain valuations, at least at the high-end, amongst rational buyers.
But, as DomBuyer stated, sometimes it can become an emotional purchase....just like a nervous bachelor forking over 2 month's salary for a diamond ring!
