Is the content caching or not?

[pmeenan]

WebPagetest isn't checking for the cache-control: must-revalidate header which your requests have. That's basically breaking the caching and forcing the browser to do an if-modified check for all of them.

Why would you want to turn the version numbers off? That is what makes the resources cacheable. Since you're on wordpress I'm assuming it's being done by a plugin like W3 Total Cache.