There's a very good reason why the high-traffic boards all generate html at post time. The content is going to be exactly the same every single time the page is fetched, and reads happen
much more often than writes. The way imageboards are structured makes it dead simple to offload the page-serving to a fully static server on a different subdomain than where the form submissions are handled. Static content can be served
significantly faster than dynamic content,
[1] this makes for a major reduction in server load and allows for many more page views on modest hardware, lessening the budget for running the website.
Now, most Shitsaba installations are used by about ten people, so this is all irrelevant in those cases, but for larger boards such as 4chan, generating pages ahead of time makes a tremendous difference, and removes the need for typically flaky and awkward (and overly
ENTERPRISE) "solutions" such as stuffing a caching proxy in front of the server. If the affected files are simply regenerated when they're changed, there's no need to constantly fuss with revalidating or invalidating the cached copies, and the problem of multiple requests causing simultaneous cache misses never even occurs.
References
1. http://arnisoft.com/239/server-benchmark-apache-nginx-cherokee/