Curious question about Lightroom previews and Camera Raw Cache

Question

Posted in the Flickr Lightroom Group as well:
I have noticed something about the Lightroom (3.6) previews and Camera Raw cache that have me puzzled.
I create a brand new empty catalog and purge the Camera Raw Cache.
Then I import ONE Nikon RAW (NEF) file with dimensions 2592 x 3872 (10 megapixels - 10,036,224 pixels).
Next I export that NEF file to an uncompressed 8-bit TIFF file. You would expect the size of that TIFF file to be roughly 30 megabytes (10 megapixels x 3 bytes per RGB value) and in fact the TIFF file is 30,135,830 bytes in size. If you export the same TIFF file but specify ZIP compression the resulting file size is 10,834,038 bytes. Obviously the compression obtained here is going to be highly specific to the image but so far no surprises.
During import I specify render 1:1 previews and I go into Loupe mode and view the entire image at 1:1 size. I also visit the develop module and do a bunch of manipulations on the image but no cropping.
At the conclusion of all of that I exit from Lightroom and examine the size of the Camera Raw Cache folder as well as the Lightroom previews folder. It would be my expectation that the previews folder  should have a rendered full image and that the Camera Raw Cache should also have a rendered form of the raw data. What would you expect the size of those respective folders to be?
In fact - in my trials the previews folder totals a mere 1,675,264 bytes and the Camera Raw Cache which contains one DAT file corresponding to the one cached image is merely 267,374 bytes. This does not seem like nearly enough bits to preserve the rendered image nor is there a full size image tucked away in the actual catalog either - that file is not large enough to contain that. And yet I can use Loupe mode at 1:1 size and move from image to image with no loading delays (even when importing multiple files).
I'm wondering if I've missed something obvious in my analysis and if not, whether someone might care to speculate as to what magic Adobe is practicing here. Even if we grant them some special algorithm to compress their previews I don't see how they can achieve a compression so much greater than the ZIP-compressed TIFF file achieves.
And for those that might think to ask - I've repeated these experiments with multiple raw images and on both the PC and MAC platforms.
I look forward to some answers or interesting theories or perhaps someone might replicate the experiment and report findings.

Answer 1

MadMan and Hal - thanks so much.
So that was my D'Oh moment of what I was missing - the use of re-rendered JPGS as previews. That certainly does fit with the file sizes I am seeing. I had naively assumed that the previews might have tried to preserve the full fidelity of the image - But as you suggest that full fidelity is likely only there in the develop module.
This perhaps explains another observation from the Develop module - moving from one image to another might display "Loading" either briefly or across a longer duration. My guess is that the length of the loading process might have to do more with what is cached in RAM than cached on disk in the camera raw cache. More of a shame then that 64-bit Lightroom on 64-Bit Windows cannot grab more RAM than it seems to do at present.