One possiblity that the FDA is considering (and it is high up the list) is
that Melamine, when added to poor quality or market - unacceptable wheat
gluten, significantly (and falsely) raises the qualty of the analyzed (by
spectrophotometry or specific gravity ?) product.  Thus the Melamine has
been intentionally and criminally added to the wheat gluten.  The big
questions on my mind are:  1)  Why were these North American Pet Food
producers going all the why to China, when both Canada and the U.S. have
abundant wheat harvests?  Answer = greed.  2)  Will the Chinese government
consider this a problem for their foriegn trade?  Answer  Probably not, as
they are doing big time business anyway and while given great importance
here, the wheat gluten problem _ may not_ be considered as significant (or
provable) there.
3)  Have North American manufacturer's learn a lesson?  If one uses history
as a guild the answer is NO.  It will be blamed on the Chinese and after the
firestorm is over our manufacture's will go back to similar sourses for
wheat gluten.  While this may sound illogical, the big pet food companies
_probably_  run on stock market controlled automatic transmissions, not
logic.  It is easier to shift PR gears than business practices.