Otherwise the file system is far superior for every "benefit" they list. And far easier to work with other software and more robust over time (nothing to change/break).
From what I remember, this was an atomic operation, and if there was a download in progress it would continue using the old file, because the data was still on disk and the filename was simply a pointer to the node.
This may behave differently on other file systems. This was done on an old Linux server with ext3
Seems like a simpler solution than using a db
I think the bigger benefit though is the increased read performance on many small files (saving system call overhead). To which amount that applies to static files that a smart server might keep in cache, I don't know.