Admittedly it's been awhile--1983 to be
exact--since I actually studied this work in a musicology
class so my memory may be a bit fuzzy.
But I
think you guys may be interpreting the "theme and
variations" genre as "character variations". Another
variation form--and generally more reespected by old-time
musicologists [read: German born-trained-or bred]are variations
that derive from a germ motive, phrase, leitmotif,
whatever and are then inverted, retrograde,
retrograde-introverted, whatever. Berg's "Chamber Concerto" is one
example, a better-known one is Brahms' "variations on a
Theme by Haydn". If you listen to the variations, the
St. Antoni chorale is very evident in some of them
and hidden in others. Another example is Benjamin
Britten's Variations on a theme of Frank Bridge; the
variation called "Chant" bears only a slight resemblance to
the original theme.