FileDirectory was updated in 2009, but since Pharo had already forked off Squeak prior to that you didn't know that FileDirectory was already a lot like FileSystem is today before anyone knew FileSystem even existed. Today these examples are almost identical.
Example #1: file := FileDirectory directoryEntryFor: '/path/to/file'. FileDirectory extensionFor: file name.
vs.
file2 := '/path/to/file' asFileReference. file2 extension.
file := FileDirectory directoryEntryFor: '/path/to/file'. file extension
#2: (FileDirectory on: 'path') entryAt: 'nohup.out'. vs. 'path' asFileReference / 'filename'
(FileDirectory entryFor: 'path') / 'filename'. I agree we should add String>>#asDirectoryEntry to avoid the keyword message and parenthesis, so both examples would be just as nice as FileSystem: 'path' asDirectoryEntry / 'filename'. I think we agree about what good design is, we just differ about which path to take there, the more-compatible or the more-beautiful path.