I'm Statamic's founder, so hopefully this answer will be helpful :)
Statamic 1.6.x keeps a cache file of all the YAML data for all your pages and entries (markdown files with front-loaded YAML). It's stored as a single big php array and updated when files inside your _content/ folder are changed. This lets you have a really high performance site under most conditions.
Statamic 1.7 (not yet released) will break the single cache file into one file per folder (e.g. /blog/, /news/, etc), which will keep any one cache file from getting too large -- an issue present in about .1% of the users.
Does that help? Anything else I could answer?