Unless the file IO is done correctly, even the best file system won't save you from data loss, such as the kind that can result from sudden power failure, which is what the article talks about.

PG obviously thinks RDBMSs are just unnecessary middlemen between you and the same file system. He doesn't realize that even if they ultimately use the same file system you do, they likely don't use it the way you do. Maybe Viaweb used something like the last snippet of code in the article, but I doubt it.