"Finally, we’ll assume single-core servers"... isn't that rather like working out mathematically that the best gait for horses is hopping, provided you assume a one legged horse?
For the level of analysis in the article, there's really no difference between a 4 core machine and a processor with a 4x clock speed. His point is that the threaded model makes the most sense when each request is CPU intensive, and the event model works best when the work is light but the delays are long. All that would change for a multi-core processor is the definition of when the works starts to be CPU 'intensive'.
Edit: My point is that, since we live in a real tangible world, where CPU power is being expanded by parallelism rather then increasing single pipeline throughput, we have to deal with that reality. To dismiss it to prove your point, seems a tad bit naive.
An evented server (at least, until they get a lot fancier and make you program with locks and such) only gets to use one of the cores, while a threaded server gets all four.
Using a single core just means that the threaded server doesn't get any advantage from being threaded, while the evented server gets everything it can use.
This "model" is worthless for comparison.