Well for one thing, consistancy is always important. In addition, this type of mismatch cost NASA a few million dollars in 1999, so it is a valid concern (see Mars Climate Obiter).
I just went from being a programmer (who does work with XML) to being a programmer and part time document specialist after a co-worker left. One of the projects she was working on was a form with several dropdown boxes, one of which had 50 items. I had to make a simple change to all 50 items. It was much easier to open the XML in vi and make one global substitution than it was to edit all 50 lines through the property palette. Yes, it would make sense to break the list into smaller ones, but I had to do as I was told.
Now, I've just been given a similar assignment, with lots of dropdown boxes with many selections each. So yes, unless I'm missing something, I will be interfacing with the XML when it is the easier of the available options. Now granted this won't involve the size issue I asked about, but I've hand coded GUI screens before because it is usually much easier than using point and click tools. So I may find it easier to position and/or resize objects by code than by GUI. Since I've dealt with Imperial measurements all my life, I would find it much easier to do so in the units of measuremnt that I am most familiar with.
So again I ask, how do I get the XML to display in inches instead of millimeters?