When you're experimenting with a new technology, everything looks very different and everything looks new. When you look at the net result of people experimenting with it 30 years later, you can see that they were all constrained by the same limitations, and in aggregate - despite many differences - everything takes on a recognizable aesthetic that was produced by the limitations of the day, the technology, the genre, whatever.
These sites are all wildly different and extremely creative, yet they're all recognizably from the same decade or so.
Okay. Now step back from that. Humans - you, me, everyone - have learned a very complex visual language from birth, where certain cues indicate certain things and trigger certain memories. If you show me a picture of a dude wearing bell bottoms, we're probably in the 70s. If it's a girl with a nose ring and a midriff showing it's probably 2005 - but there are smaller cues within that. 99% of people don't think about this consciously when they see an image, or a website, or whatever. They just associate it with a time or a genre.
In design for the web, we've had decades of constraints come and go - we had Flash with its own weird aesthetics, Java embeds, etc. People remember a time and they associate a design style with that time, without really knowing why. So it's a question of choosing from that historical library and constructing something that makes people see what you want them to see. If you want them to associate something with the early 90s, then totally make it look like one of these pages.
The thing I was taught in design school was to attempt to make design that was timeless. This is always kind of impossible - because you're limited technologically in ways you don't even realize at the time, and because you're always influenced by what's around you. But try to make something that will look, in 20 years, like it was new. Very hard to do. Why do it? Because in 20 years, you can always go and make funny vintage pastiche references to what people did 20 years ago. But it's quite hard to make anything that doesn't show its age.
