Tom,
Since baker's percents work with weights only, all the Lehmann recipes that are based on baker's percents are recited by weights. That includes liquid ingredients also, like water and oil. Because most cooks are more used to volumes instead of weights and are unaccustomed to using scales to weigh things, I try as much as possible to convert the weights of all the ingredients in the Lehmann recipes to volumes.
For liquids that can be measured in a measuring cup it would be possible to use, say, 4 fluid ounces instead of 1/2 cup in a recipe, but the word "ounce" in that context might confuse some. Using fractions of a cup are less likely to do that.
You asked whether it makes a difference whether weights or volumes are used and the answer is yes. If you look at the document for which eric22 provided a link above you will see that 8 fluid ounces of water weighs 8.3 ounces but 8 ounces of honey weighs 12 ounces.
As far as how to cope with high altitudes situations, I don't know that there is a way of compensating for altitude in recipes, as by modifying the amounts of certain ingredients. As you know, in high altitude situations the usual advice is to decrease the amount of flour in a recipe, or to increase the amounts of liquids, or use less yeast. I suspect that this is something one must learn to do from experience.
Peter
