The "natural speed" of most digitals is 200 ISO and there is no gain in image quality at 100 as opposed to 200 as there is with film - the opposite, if anything, is true. Granted there are times when it is necessary to drop below 200 for exposure reasons and the situation being debated here is one of them. My point is that there is no good reason to operate any digital below 200 ISO as a matter of course, particularly with modern studio stobes that can mostly be throttled back to at least 1/32nd power.
Digital doesn't work the same way - most if not all digital cameras can't be set slower than ISO 100. Period.