cpmCPUTotalPhysicalIndex is used in IOS devices with multiple CPUs to put the information stored in cpmCPUTotalTable together with the information stored in the entPhysicalTable.
With this mapping you find out which CPU index is used for which pyhiscal CPU.
If the device only has 1 CPU, it is clear for which CPU the statistics are collected and thus cpmCPUTotalPhysicalIndex does not give you any further information.
have a look at the following document to get a better understanding:
http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080094a94.shtml#multiple