Apparently the small print referenced here should have been one clue: Does InstallShield Limited Edition Support 64 bit Installer?
The current Office prerequisite in Installshield is also misleadingly worded. It should really be "Office 2010 Home & Professional 32 bit".
Perhaps they intend to upgrade it over time to be comprehensive or perhaps everyone has to go through the same hassle to fix it for a few cases they care about. The support guy claimed there are too many GUIDS for all the combinations of versions, bitness, releases etc.
Home & Student, Home & Professional, Professional, Office 2010 Professional Plus License 32bit, 64bit, Languages mangled in there, Service Packs, etc. Depending on the set you care about the number of GUIDS is rather large.