(a) PRP (like HSR described in IEC 62439-3) is a solution that provides seamless redundancy through completely doubling network topologies (which severely limits financial feasibility) and introduces a dual connection mechanism that is not compliant with IEEE 802.1 bridging.
RSTP and its specific application in a ring topology described in IEC 62439-1 still is a mechanism that relies on network reconfiguration and introduces communication outages to whole networks or parts of the network. This is in conflict with the main requirement of the proposed PAR, enabling seamless redundancy without any loss of communication.
(b) No, the IEC 62439-3:2012-07 spec revision does not change any of the fundamental concepts of the PRP and HSR protocol described in this document. It merely corrects mistakes e.g. in the MIB and adds additional material throughout the document (e.g. HSR to PRP connections) to clarify questions and ambiguities reported to the IEC SC65CWG15 group by implementers.