you are wrong:

The replace command uses record locking in the same manner as the update - SQL command when you're replacing just one record. The main difference is that if you use these commands to replace more than one record the update uses multple record lock and the replace command uses a file lock. The replace command blocks more records at a time and the lock last longer than the separate record locks of the update command. The update command garantees a higher degree of concurrency, but is slower than the replace command because it has to lock each record before it is updated.

For best performance: use replace
For best concurrency in a multiuser environment: use Update - SQL

I think the main reason for including the update command is that it is a ANSI SQL command. (See the differenct between the DELETE and the DELETE - SQL command)