I've been on the front page of HN multiple times, you won't even come close to the $5 limit of 1 TB. This is ridiculous.

Different if you're on the front page of reddit, or on some popular subreddit. If you don't have all static files on a CDN you can easily exceed 1TB within a few days. Assuming it's a side project that you're not constantly monitoring and you're away for a few days, you could find a hefty bill when you come back.