Not all Content Preloading

Since noticing this in an earlier thread, I've been looking at how Storyline content preloads and loads using HTTP Watch.

According to this Storyline KB article, assets should preload:  http://www.articulate.com/support/kb_article.php?product=st1&id=1ah88m0ttqbd

However, If I'm looking at things correctly with HTTP Watch, they may possibly not all be preloading.  Narration files as MP3's appear to be loading real-time when the slide is accessed.  Most everything else gets pulled from cache.

And every so often, a occasional graphic or SWF file also appears to load real-time instead of coming from cache.

Am I seeing this correctly?  Do some assets really not preload?