They were all established / founded in the early web. I'm not saying that there was not competition, or that their success was because they were first - they still gave superior products which beat any rivals at the time.
However, trying to draw parallels with these site's design and success today is not totally relevant. If you launched either of them today as they were / are, they may not succeed (despite as we know, the core product / service / functionality being great).
Rob Walling writes in his book that these days: 'It's Market(ing) First, aesthetics second and functionality third'.
Firstly you need to have a market for your product and hopefully be able to market it well enough to get people to 'want your product' / know you exist.
Then when they look at your site, you need the aesthetics to give a first impression of your product and gain trust from your customers in your product. It doesn't matter if your service / functionality is brilliant. If you can't get the user to even try you over any competitor, then you've wasted your time.
Then thirdly, if you're lucky to achieve the top two - give your customers a good user experience / functionality they want, so hopefully they pay / keep coming back.
The reason the sites given in the example can happily remain ugly, is because they already have the user's trust and are a known 'experience'. Therefore the aesthetics don't need to work as hard to make an impression as say a newly formed start up today.
- EDIT... I'm not saying that a site which is kept basic in design can't be successful. Infact, I agree quite heavily with the principle of keeping things simple and have blogged about it in the past.
Perhaps the original author should've done the article on one of the many great sites over the last few years, which have embraced this 'Keep it simple and clean' attitude. Hacker news being a perfect example.