Nope, look at the edit interface... he does auto-discover most slashcommands (including the game defaults)
You're getting confused by his example screens.
Edit: Unless you meant that he doesn't auto-associate with the addon name, which you'd be right about
But he does produce a more or less full listing of slash commands available in the edit dialog.
Edit2: To clarify further he's iterating through SlashCmdList internal Blizz table which addons use to register their commands.
Anything that uses SlashCmdList["myaddonslash"] = MySlashHandler will be listed.