Number-based organization systems (e.g. US code) work best when there are frequent references to specific nodes in the hierarchy (e.g. legal citations) and there is no guarantee that they're being accessed digitally.

But there is a good reason why I navigate to news.ycombinator.com and not 209.216.230.240.

For digital resources like URLs or file systems, using numbers as prefixes or primary IDs only makes sense if their ordinal values represent the most important and intuitive way to browse through the hierarchy.

But in most cases, the name rather than the number is the most important thing, and it's very easy to sort or filter by name -- whereas sorting or filtering by number is only useful if there's an inherent ordering (e.g. date modified) to the numbers.