The latest blog postings and the blog feeds are updated by 2 different cron jobs.
The tools/cron/jobs/10/1gen_blogs.php cron job is what updates the blog posts.
The tools/cron/jobs/10/gen_feeds.php cron job is what updates the blog feeds.
The tools/cron/gen_blogs_full.php file only updates the blogs and postings, it doesn't update blog feeds.
The problem with the blog feeds, if your cron jobs for whatever reason aren't working properly (or even crap out temporarily), it get's lost and won't get written to xml feed file. It's always been a bit of a problem from day one without any real solution, and why I never used blog feeds on the site, they just aren't reliable enough and can't be updated or regenerated if something goes wrong with the cron jobs.
You rarely have this type of problem with news feeds because they're instantly written to the xml file in real time, and don't rely on cron jobs. Unfortunately you can't have blog feeds written to the xml files in real time because on a busy site there's the potential of writing a lot of blog posts and comments, which would have an impact server resources.
My best guess is that your cron jobs possibly crapped out for whatever reason which means blog feeds won't get generated.