The WXDailyHistory.php will try to get a complete 'yesterday' daily file (when run on a specific day), and a complete prior-month file when run on a 'month' display. Generally, random traffic to the page will keep the day and month files up-to-date. The 'week' file is ever-changing, so updates when requested by the WU-History page. The 'year' requests are just an accumulation of up-to 12 month files, so may only result in fetching the current month (for current year) requests. Prior year requests are generally from the cache, and only refreshed if you delete a cache file.
So, no, I don't have a cron running to keep the cache refreshed - just organic traffic to the site (including web crawlers) is generally enough.