What doesnt make sense about it? Generally, they all share the same baisic design, the only difference (generally) is the bore, stroke, and casting materials. In modern times, all of the LS engines are aluminum, while the LQ engines are iron. Take for example the LS2 and the LQ9. Both are 6.0L engines, share similar designs overall, but the LS2 is aluminum and the LQ9 is iron. One makes 400HP, the other 345HP.
...There isnt anything confusing about GM's small-block lineup. If you want confusing, look up the different variants of the I4s at Honda. Whats the difference between a B, H, K, etc. class engine?