Peter:
In my limited understanding of ExcelXP, I think the issue has to do with how Microsoft respects or does not respect style information. The SAS style template goes into building the in-line style section for the ExcelXP XML file. Then the style overrides that come into the picture, via the procedure syntax are put "down" in the tag for the cell or element itself.
I think that Microsoft, by design, mostly respects what comes in via the in-line style section. I do find that backgrounds and foreground colors, fonts, formats and cell types are generally respected when they come into the XML via a style override (procedure syntax) -- but very frequently alignment seems to be ignored.
Although it may seem like the PROC TEMPLATE method is convoluted, do remember that if your PROC PRINT was followed by a PROC GLM or a PROC REG or a PROC MEANS, that their headers would ALSO be affected by the STYLE template and since they do not have any internal syntax to change their headers, this is a good thing.
cynthia