Pretty much. The higher the concentration, the less water. The lower the concentration, the more water. The actual amount of Sodium Hydroxide doesn't change.
There can be many reasons why someone would want to use more or less water. I normally use 33% Lye Concentration, but because I live in the Pacific Northwest where it rains a lot during the winter months and I cure in my garage, I use less water (35%) during those months elsewise I have to add three weeks to my cure time. Some folks with a higher Lye Concentration as there is less water to evaporate and they can shorten their cure time, but you have to realize that there is more to "curing" your soap than water evaporation. There is what is happening on a molecular level that produces such a great bar of soap.