To the best of my knowledge, a different strain is used for the dry yeast products. It is still S.C. but just a species that is better suited to the drying process, hence improved yeast survival after drying. Since there are literally millions of different strains of yeast available to choose from, this does not surprise me in the least. There are also some select strains that have a thicker cell wall and as a result demonstrate improved survival/performance in a frozen dough application. Remember, it's the ice crystal that forms inside of the yeast cell which with slow freezing, can grow to such a size as to puncture the yeast cell wall thus reducing its survival and/or performance after the dough is thawed. The thicker cell wall is better capable of resisting the damaging effects of the ice crystals.
ADY is a good product, but it does have some shortcomings, it does not exhibit the consistency in performance needed in commercial applications, but in home applications these differences just can't be seen, not that they aren't there, but who at home ever complains the the dough took an extra 5-minutes to rise to a certain height than it did a week ago? That CANNOT happen in a commercial setting since it would upset the entire timing of the bakery. IDY, on the other hand was actually developed for the commercial baking industry, not here in the U.S., but in Europe, hence more attention has been focused on achieving a consistency level of performance, which it does demonstrate. We have done numerous real world tests on the different brands of IDY and all of them are so incredibly consistent that over a three year testing period control doughs ALL and ALWAYS gave final proofing times within two minutes of the fixed target time (60-minutes). That is a plus or minus of only one minute for doughs that were made by the 70/30 sponge-dough process, given 3.5-hours of sponge fermentation, mixed to full development, given 15-minutes floor time (rest) then divided, given 10-minutes intermediate proof (rest), molded, panned, and given a final proof (rising) at 100F/85% R.H. with a targeted time of 60-minutes. The consistency with the IDY was significantly more consistent than we ever got when using compressed yeast (which in reality is rather variable) giving a variation in the plus or minus range of 3F. ADY was in the range of plus or minus 6-minutes. In a home setting where dough absorption is not controlled, dough temperature is not really controlled in most cases, and room temperature varies considerably, not to mention scaling accuracy, not just with the yeast, but with the other ingredients too, is it any wonder why we don't see these differences? But with that said, those differences still do exist.
Tom Lehmann/The Dough Doctor