OK, I did some research and I don't think the sulfur generation is normal or desireable.
The source, as far as I can tell, could be wild yeasts in the juice starting to ferment or the production of H2S from a combination of factors, most likely the wrong yeast, lack of racking, etc.
I make fruit wines as well as beer. My textbook for fruit wines is this:
I've never had an sulfur smell from any fruit wines that I've brewed.
As far as the wild yeasts go, on page 238, it states to add 80 to 100 ppm of sulfite to "kill wild yeasts prior to fermentation". I add sulphite crystals as directed to all the fruit wines I make.
One has to remember that fermenting wine musts is different than fermenting wort. Wort has just been boiled and it and the container is sterile. Fruits are exactly the opposite. They are simply washed and used. They are loaded with bacteria, organisms, etc. Never the less, I strongly suspect that the apple juice from the store is basically sterile.
I think the real problem is the fermentation conditions.
Page 267 says this:
"Hydrogen sulphide is created by wine yeast during fermentation and some strains such as Montrachet, produce more H2S than others. Generally the problem is not apparent until the secondary fermentation stage. During the secondary fermentation, the dead yeast cells build up in the sediment, and as they break down, their natural sulfur content is reduced to Hydrogen Sulphide. The heavier the deposit and the warmer the temperature - the greater the probability of hydrogen sulfide developing."
It goes on to say that if the smell stays in the wine for longer than a week, it changes to other substances and ruins the wine.
aeration, adding sulfur dioxide, adding copper sulfate. According to them, these are only make shift actions.
Use a different yeast. After INITIAL racking, don't leave the wine on the yeast more than 10 days. For these authors, initial fermentation is done when SG hits 1.020 or so and they rack to a secondary fermentor at that point.
They don't say it, but fermenting at a colder temperature will help as well.
All their apple wine recipes use a champagne yeast. (Bayanus Champagne.)