I have doubts about their long-term value. People enter actual urls less and less, eventually I can see the browsers ditching them completely (from the presentation layer), and then you might struggle to find anyone paying millions for .coms. Likewise the marketability of a 'dotcom' brand might fade like tech terms often do (remember when everyone used to boast about having 'CD-ROMs').

I thought a lot of the value came from SEO. I just googled "sex" and sex.com didn't come up at all. That could be because they have a link page up instead of any content. Googling "slots" at least brought up slots.com 6th.

In terms of being top of their industry, I would think that spending this kind of money on a domain would be accompanied by the conscious or subconscious thought that since we have such an amazing domain, we'll coast and let the traffic/money come in, vs. obscure domains/company names who have to earn traffic by proving their value.