I can understand how an established name can fetch a high price due to the traffic it would already have, but I don't understand why an individual would be willing to pay 10000% or higher markup on a string of words, even if the hit to their bank account lessens over time. If I want to start a business called My Web Hosting, what difference does it really make if I choose mywebhosting.com, myhosting.com, my-web-hosting.com, webhosting.com, my-hosting.com, hostforfree.com, cheapasshosting.com, etc? Even if one or all of those were taken I could pick a name that would work just as well without having to pay a premium on it. It seems to me like promotion is more important than the domain name anyway, as sites like craigslist.com, dmoz.org, and wikipedia.com have names that mean absolutely nothing, yet everyone knows about them anyway. Hell, wikipedia got well over $700K in donations last year.
For a corporation it isn't a big deal because for them $100,000 is pocket change, so $100-10,000 for a domain name is nothing, especially over the long term. It's a cost of doing business (and a handy way to quell dissent, as in the case of Wal-Mart acquiring walmartsucks.com). Even then, however, you have some of them going with discovercard.com rather than discover.com (as an example).
And those are just relevant domains. I see people literally stringing together random letters and numbers and trying to sell those off. That and domains with extensions that most people are unaware actually exist (.info, .jobs, etc). I honestly can't see how any domain other than a top-level domain would have any resale value at all unless it was a country domain and you were marketing locally.