Websites come, websites go. But are they really gone? Not always. There's something called The Wayback Machine, where you can retrieve old versions of current, or even defunct websites. It's not every page, and it's not every version of a given page; some companies block access to their pages.
It's not just curiosity, though, that fuels the Wayback's usage. Once, I had a question that involved accessing a form or document from the Bureau of Indian Affairs website. For some bizarre legal reason, the BIA page was blocked, but I was able to access the piece using the Wayback Machine to get an earlier version of the BIA site.
Here are 50 Fun Ways to Use the Wayback Machine.