The approximate (5.0 MB) size really is "approximate." RAW shots will vary in size depending upon several factors. The LCD display shows a potential 29 shots for a Lexar 256MB when using my D100 - which shares a similar 6.1 MP CCD sensor. Note that the number of remaining shots really is an estimate - you may get more or less depending upon your processing settings in-camera.
Download the D-100 owners manual but as I recall, that manual lists the RAW files as about 9.8MB which would allow about 25 images on a 256MB CF card. I think the 5.0MB number is a mistake in the D-70 manual.
The math is wrong. The D100's raw size is nearly double the D70 because D70's raw files employ Nikon's apparently revolutionary new raw lossless compression. The approximate size of these files is 5.9mb. That is why capture 4.0 is incompatible with the D70 files because it is a new lossless raw compression unlike the D100's lossy (data lost but imperceptibe to the human eye) raw files.
Doing the calculations for the other entries in the table (refer to 12-page D70 brochure available from digitalreview.ca and elsewhere) file size x number of available shots are all in the 200MB ball park, which is fine. The calculation of 5.0MB x 23 shots = 115MB which is quite low, even with variation in mind.
The D70 also features an improved hardware buffer that is far superior to the D100 (at least according to all previews and initial hands-on experiences) when handling compressed RAW, so it's natural to take advantage of this format first to maximize CF storage.