Both Intelligent Updaters (i32 vs v5i32) apply the same virus definitions. They are not dependent, to the best of my knowledge, on the processor, only the version installed (SAV vs. SEP).
To clarify, the i32 installer is not necessarily delivering Rapid Release definitions:
http://www.symantec.com/business/security_response/definitions/download/detail.jsp?gid=savce = Certified definitions
http://www.symantec.com/business/security_response/definitions/download/detail.jsp?gid=rr = Rapid Release definitions
There was an issue similar to what you're experiencing in an earlier build but that was resolved with MR4 MP1a. I'm not aware of any issues subsequent to that.
Intelligent Updater fails to update definitions when using the Version 5 updater.
http://www.symantec.com/docs/TECH92633
I suppose it is possible that in the case of an older machine, the operating system has been up and running so long there is file system degradation or incorrect file/registry permission somewhere along the line. Just a thought.
sandra