The Detect Alignment spell text tells us that "only divine spellcasters, undead, and beings from the Outer Sphere have an alignment aura if they are 6th level or higher". Therefore, divine spellcasters, undead, and Outer Plane creatures of 5th level or lower don't have an alignment aura. The table for Detect Alignment on the same page, however, tells us that "clerics and other divine spellcasters with a patron deity are treated as 5 levels higher, as are undead and creatures from the Outrr Planes". With the exception of 0-level undead such as skeletons and zombies, every single such creature's minimum level is 1, therefore they are treated as a minimum of 6.
So, I can only see two things to conclude from this. Either, the text and the table do not contradict each other and they are written the way they are to account for the corner cases of skeletons, zombies, and divine spellcasters that DON'T have a patron deity (Monks that use divine spell powers and demonic or angelic Sorcerers). Which seems like an odd distinction to make in such an obscure manner. Or, the text and table are telling us different things.
Which is it?