Jake--as an archaeologist who has a very strong academic background in
architectural history (Ph.D. in architecture), I think determining function
is a legitimate goal when looking at structures or structural remains.
These objects are part of the site, and one of the major archaeological
goals for most, if not all, sites is to determine function.  And yes,
functions may change through time and original function or interim functions
may be unknown (at least from the historic record).  But we can certainly
produce some intelligent theories as to what a structure was used for at one
or more points in time.  And maybe the bottom line is that this is another
case where archaeology can amplify or clarify the historic (and
architectural) record.
 
On a closely related topic which may interest the list, I recently read an
otherwise very interesting book on the architecture of St. Augustine,
Florida which traced the changes in architecture through time and relates
them to the historic changes occurring in the city.  There were several
references to archaeological studies throughout the text.  But the final
paragraph in the book slammed archaeologists.  It stated in essence (and
this is paraphrased since I don't have the book at hand) that while
archaeologists undoubtedly obtain a great deal of information which could
aid in identifying the architectural history of both individual structures
and cities as a whole, this information was buried in obscure documents
written in jargon that only an archaeologist could understand.  So list
members--are we guilty as charged?  I hope not.
 
                                Lucy Wayne