Of course, all this really lets you do is survive a swarm of people from (for example) here, digg, a tweet meme, stuff like that, which will direct everyone at one single page on your site.
But I think that's the most likely cause of that kind of traffic on a small cheap VPS, as anyone running a big site without clustering is just being silly :)
Yup, that's fair. And there are actually ways to scale WP beautifully with a small amount of servers (we're using less than 5 servers to handle our 10M visitors a month and content archive). Again, I keep meaning to blog about it, I just need to find the time.
Anyways, I'm all for articles like this that help optimize WP sites and get rid of the stigma that WP doesn't scale without cost. Thanks for writing it.
Hope I see a blog post from you about it sometime soon, I think the details around that kind of stuff are far too hard to discover for people trying to learn about it.
But I think that's the most likely cause of that kind of traffic on a small cheap VPS, as anyone running a big site without clustering is just being silly :)