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I can't speak for Mr. Goldfarb. However, my feeling is that he meant that when the film is exposed using the manufacturer's recommended ISO speed - that the film will accomodate 4-5 stops (Zones - however you want to look at it) of exposure range. The limiting factors being the film D-max and the gamma (slope) of the film's response curve.
As an example, I would suggest that anyone looking for a dramatic comparison in film response (and resultant film range), look at Kodak E-200, and Fuji Velvia. You couldn't find two more different films even though the D-max of each is almost identical.
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That's what I meant Steve. With most slide films, you can register detail over a 4-5 stop range when the film is exposed normally. So if you've got a scene, with important highlight detail that is 6 stops above the most important shadow detail, you'll have to choose between them or shoot negative film or change the lighting with additional lights or reflectors.
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Slide film will have a certain latitude, or range of stops (zones) it can comfortably "cover". Some people call it a "scene brightness range" or SBR. Often, the important parts of what you want to shoot will be within that range. If so, then it's great. But, sometimes the contrast is higher or lower. Then you can use a different film if you have it with you. That's why there is Astia and Velvia - one tones down the contrast and the other really bumps it up. As far as the basic idea, it is the reverse of print film. For a negative you expose for the shadows (zone 3). With slides, you expose for the highlights (zone 7). A lot of times you then have to decide what you want to keep, and what you will allow to block up or blow out.
