Perhaps this is just a matter of perspective. I'll use one of the more familiar examples of zeugma, from Pope's Rape of the Lock:
This Day, black Omens threat the brightest Fair
That e'er deserv'd a watchful Spirit's Care;
Some dire Disaster, or by Force, or Slight,
But what, or where, the Fates have wrapt in Night.
Whether the Nymph shall break Diana's Law,
Or some frail China Jar receive a Flaw,
Or stain her Honour, or her new Brocade,
Forget her Pray'rs, or miss a Masquerade,
Or lose her Heart, or Necklace, at a Ball;
Or whether Heav'n has doom'd that Shock must fall.

Pope uses zeugma in a couple places here, most obviously with "stain" in the 7th line here, and "lose" in the 9th. Since zeugma uses more than one sense of a word, it takes an active reader to realize it, just like with a pun. The reader or listener's imagination must be actively "creative", not relatively passive like it could be with most of the other lines here. The sense is not straightforward -- so it requires an audience to untangle it, just as it required Pope to tangle it in the first place.
     I would suggest the same activity is necessary in reading TWL. The following two lines are perfectly understandable on their own, since they are both in English:
Shall I at least set my lands in order?
London Bridge is falling down falling down falling down
However, when the lines are put together, a new meaning is created, and the reader must try to understand their connection. Hope this helps.

>>> [log in to unmask] 10/08/03 06:48PM >>>
William Gray wrote:

>    According to the descriptions I remember, I would classify TWL as a cool medium. Structure of juxtaposition, like that of zeugma in the 18th century, requires audience participation in order to function.
Dear Will,
    I know zeugma as a rhetorical structure (and cool word).  It is one
of a seeming infinity of juxtapositions.  But I don't know anything
about the 18th-century use that requires audience participation.  Tell all.