We shouldn't
access the filesystem…
I don't know who you're referring to, but just in case you don't recognize /dev/fd, on BSD it seems to work the same way as /proc/self/fd. **EDIT**: Take this with a grain of salt--they might not be symbolic links, so not a complete replacement.
Yes, I'm aware /dev/fd is a symlink to /proc/self/fd on Linux. But, again, this is Linux-specific. (Is it part of LSB?)