DNGs and RAWs aren't generally (AFAIK) uncompressed. But ideally they're losslessly compressed. They're all(?) "TIFF files" - but AFAIK saying something is a valid TIFF, is almost as helpful as saying something is "a file".
Apparently Sony uses some kind of lossy compression for it's files - I just tested with a jpeg2000 encoder on the same file above, and the size of the j2k file is approximately the same as the ARW: 7MB. Btw, the lep-file is 1.7MB.
Note that the uncompressed (flat) PPM file is 29MB as is the uncompressed TIFF - but simply running the TIFF through lzma reduces the size to 9.3MB. So ~7MB isn't that far off.
[ed: And while the lep-file was 1.7MB, shaving a bit off the original jpg, mozjpeg with defaults+baseline created a jpeg (at q=75, per default) 472k in size. Lep managed to shave a bit off that too - ending up with PPM->mozjpeg->lepton resulting in a 359K file. The (standard) progressive mozjpeg ended up at 464K.
This is not quite apples to apples, though, I think the comparable quality setting for mozjpeg would probably be 90 to 95 or so -- ending up around 1.6MB. But for this particular (rather crappy) image - I couldn't readily tell any difference.
Raw files store only one channel per pixel. A TIFF has been demosaiced and stores 3 channels per pixel.
On top of that, most sensible raw formats only store 12 or 14 bits per pixel, instead of 16.
And then most are compressed, some losslessly and some lossily (like the infamous Sony format that packs it down to an average of 8 bits per pixel but does exhibit artifacts).
