I don't know how much I believe that... Granted, I only have 8 breeding pairs and only 5 of these pairs has had multiple litters, but I have not found the number of kits to be consistant and they are always with the same mate.
Clyde (Standard) and Avra (BV) produced triplets with their first litter, but then had single kits for their next four litters.
Z (Mosaic) and Mabel (BV) produced triplet with their first litter and had a single kit in their second litter.
Koontz (Dark Ebony) and Bonnie (Standard) produced twins with their first litter, triplets with their second litter, and twins for their next two litters.
Kent (Standard) and Kalli (Mosaic) produced twins for their first three litters, then had a litter of triplets, and most recently had a single kit.
Harold (Beige) and Henna (Dark Tan) produced twins in their first three litters, then had a litter of triplets, and most recently had another litter of twins.
I had two Ebonies in breeding previously. They produced twins for their first three litters and then had a single kit for their last two litters.
I'm not saying that genetics don't play a role of any kind, but I think there are some things you can't just predict.
I recently read something that Gary Neubauer had said about how you'll have more females born if you keep the chinchillas in a colder climate and that, if they are in a warmer climate, they will produce mostly males. I was very interested in this theory. A friend of mine who also happens to be a breeder told me that she has only had one male born and all the rest of the kits have been female. The first thing I asked her was what temperature she kept her house at and she told me that she kept the thermostat at 75, which is the same temperature I keep my home. I guess some theories just don't always prove true, even if they are most of the time. *shrugs*