Richard:
I would bet that part of this is a legacy issue since Photo Mechanic began offering XMP support within the past two years. The field names they are currently using match, almost to a word, those in the original IPTC Information Interchange Module (IIM) schema, with the exception of the Byline/Author/Creator field, which they call "Photographer."
On the Controlled Vocabulary page devoted to the IPTC standards,
http://www.controlledvocabulary.com/imagedatabases/iptc_naa.html, I have a link to the "IPTC Core mapped fields PDF"
http://www.controlledvocabulary.com/imagedatabases/iptc_core_mapped.pdf, which shows how these field values change between applications.
What would make most sense (at least to me) is one of two things.
1. Adopt those fields that are recommended in the IPTC Core Users Guide,
http://www.iptc.org/std/Iptc4xmpCore/1.0/documentation/Iptc4xmpCore_1.0-doc-CpanelsUserGuide_13.pdf, or
2. Provide some sort of toggled preference so that the user can select the set of field names that they prefer to use. iView had done this a while back and those that only wanted to use the old fields could do so, simply by changing their preferences. While those that wished to embrace the new IPTC Core/XMP style fields could do so if they wished.
If you take a look at the IPTC Core Mapped Fields PDF I mentioned earlier, you'll see that even Photoshop hasn't followed the prescribed names implemented in the IPTC schemas (past and present), and there is a still a bit more variety than those of us in the trenches would like to see. ;-)
For those looking for a simple way to deal with this now, I would suggest that they simply to set up their template for the IPTC Stationary pad, and pre-populate from a file that has all the fields you want to use. You can either put in your preferred value, a "token" for the value you wish to include, or a reminder of what you should put there.
For those that want to know the easiest way to get their Filename into the "Object Name/ Title/ Document Title" field, all you have to do is put {filenamebase} into that field. Detailed instructions can be found at:
http://www.controlledvocabulary.com/help/cvkc-photomechanic.html#filenametitleHope that helps.
David
http://www.controlledvocabulary.com/