Skim milk is specified for the whole wheat bread recipe list included with my new bread maker. Is there a particular culinary reason to specify skim milk not skim milk/whole milk? The other ingredients are whole wheat flour, self-raising flour, salt, sugar and yeast.
Skim milk contains less fat than whole milk. Fats limit the formation of gluten in bread dough to some extent, leading to a tighter, 'softer' crumb. As the milk is apparently the only source of water in your recipe, the recipe authors could have tried to limit the amount of fat.
That said, there is also a good chance the reason for skim milk is health-related.