In short an assignment of IP rights with scope of worldwide means that all rights of IP are assigned to second party. Further it also comes to specific clauses of assignments which can restrict to exclusive or non-exclusive mode, specific patent number or portfolio. to cut short if exclusive rights are given then all IP belongs to new holder along with responsibility of maintaining and enforcing the same.
On your other query as WIPO not being filed or applicable on some country. Please note WIPO is an application only and doesnot mean that patent has been granted in designated country. Applicant has 20, 30 or 31 months to enter in designated state. Assignment of WIPO application means that new holder can file in designated state but cannot in non-designated state. Further if parent application is part of assignment and 12 months has not passed new holder of IP can enter directly into national phase using Conventional application method.
Countries having no IP or limited laws cannot be considered as it becomes out of scope of assignment if not specifically mentioned in its clauses. In general I have seen annexes of countries wherein said transfer is applicable and one can include all countries as per desire irrespective of IP laws.