FWIW, AAdvantage have a 4 segment rules as well; they appear to choose not to enforce it. BA have a similar rule and are known to be enforcing it.
As far as
oneworld goes, the following is on the One World site at
oneworld Tier Status:
... Your frequent flyer programme will require that you undertake a certain minimum of flying on the "home" airline. Please consult the programme operator for details. ...