E_S, thanks for starting this thread and VK, thanks for that excellent WSJ article (a bit of an oxymoron these days considering that they are owned by the nefarious Murdoch).
Appoggiaturas can be operationally defined as musical accents that defy our fundamental expectancy structure. This could be very brief as in the "We can work it out" example by the Beatles or in Billy Holliday's "A foggy day in London town", in the way she says "London". However, the definitions of appoggiaturas on NPR's "All things considered" were a bit narrow, so they could be more exact in the definitional/technical sense. Most of the other examples on the show dealt with appoggiaturas at a single note level.
For centuries, musicians have been playing with accentuation and resolution of the ensuing instability in different forms. Music that has the ability to do modulate consonance (within the structure of perceived musicality) has the greatest ability to induce emotions, positive or negative. Brain imaging studies have shown that such music triggers the activation of the limbic system and other emotional centers of our brain. My colleague Robert Zatorre in Montreal recently discovered that the crescendos and finales create this effect as well, related to a neurotransmitter called dopamine related to reward anticipation mechanisms.
In CM, although we don't see appoggiaturas related to harmony/consonance, we can observe them in routine gamakas and note establishments even in the absence of metric structure.
One could say Appoggiaturas are so common in CM, that we might have stopped paying attention to them explicitly. And then there are specific phrases that violate expectancies by making octave changes. I have included three non-standard examples from three very different kinds of performers below.
Let us consider the example of the sahAna padam, mOra tOpu (see link below)
http://soundcloud.com/ramesh-balasubram ... a-moratopu ; see the beautiful basic violation of the octave expectation, "tOpu" begins in the higher reaches and then the rest of the line sustains that feeling. There is also a volume change (very common in cantatas and choral music from the baroque period in Western classical music). This is an exquisite performance by Smt Sowmya in the tradition of her guru T Mukta.
Here is a second example in a neraval line for RamanAtham bhajEham by Sri NSG (see link below)
http://soundcloud.com/ramesh-balasubram ... ra-neraval
Watch how he builds the structure of the beautiful neraval line "kumAraguruha mahitam" (textbook example of sowkhyam) and then just as one gets into the trance (around 1:15 in the clip), he makes an octave change. One could classify this a case of impromptu appoggiatura. You have to listen to the entire clip to get the full feeling of the effect he manages in that last second.
Here is a third example ->
http://soundcloud.com/ramesh-balasubram ... rabharanam.
Watch the development of the sankarabharanam alapanai, where L. Shankar follows a well defined progression and at around 0:48, makes an almost cello like dive into the lower octave. Gives me the chills every time I listen to it.
So, why this effect? The brain likes things in the environment to be predictable and simple. When sudden shifts happen to disturb the steady state, we have always had evolutionary reasons to turn on our limbic system to motivate our action systems to move (fight or flight). It is likely that music is tapping into these fundamental biological mechanisms.
P.S: Standard discalimer: all musical clips are posted for academic/illustrative purposes only.
but didn't fall for it since I felt that the interval was poorly realized !