Cgiles,
I agree that, if I were a piano purist, I would never think of playing a high-end piano sample from a keyboard like the Tyros 2, with 61 non-weighed keys, that would make it difficult to control the expression of said sample. Part of the illusion of playing a real piano comes indeed from the action and this -together with the sound itself- is one of the most debated issues in other Fora, everytime the issue of the "best digital piano" comes up.
However, I have to disagree with you that the sample importing function should be used more to import vocal sounds or effects a la James Brown, to enhance the impact of a live show.

Let me make a few examples.

People keep saying that the T2 drums are too "polished" and lack the dirty quality found in other arrangers, like the Ketron SD1 or the Korg PA1 X; well, with 1 Gb of memory at your disposal you can import a ton of drum samples and build up your own drum kits, and this is a really easy task, first because you have to deal with no-looping samples and second because each sample takes just one note.
Personally, I have sampled all the keyboards and the drum machines I have had in the past. These samples reside now within my Akai S 2800 and my Ensoniq ASR 10, but they both have shortcomings: they have only 16 notes of polyphony, the Akai lacks the powerful effect section of the Tyros 2, the Ensoniq has a very poor user interface and the list could go on and on.
Now, can you imagine having all these samples within a machine like the Tyros 2?
I have recently expanded the RAM memory of my T2 to 1 Gb and have loaded all the vocal samples Yamaha made available on their website. They fill a gap the original Tyros had, compared with the PSR 9000, but I still have many other samples of vocal sounds, from almost every synth: Roland, Korg, Kurzweil...

The possibilities are endless!