As divine casters (with domains), inquisitors should require a divine focus suitable to their god or worship in order to cast their spells. So why does the inquisitors kit come with both a spell component pouch and a wooden divine focus? An inquisitor should never require a spell component pouch for their casting, so the only use I can possible see having one, is if their trying to fake being an arcane caster.
According to the SRD on magic:
If the Components line includes F/DF or M/DF, the arcane version of the spell has a focus component or a material component (the abbreviation before the slash) and the divine version has a divine focus component (the abbreviation after the slash).
So it is not an universal rule that all divine spells can substitute material components for divine focus. Spells that require material components only, without such substitution, may exist on the Inqusitor's spell list. And indeed, True Strike requires a small wooden replica of an archery target focus, that cannot be substituted for divine focus, and Force Anchor requires a twisted nail material component, again with no "/DF" on the list.
Inquisitor spells can require either a Divine Focus or a Material Component (or in rare cases, both)
A Divine Focus cannot be used as a substitute for a Material Component in any spell unless that specific spell tells you it can. There are some spells that require a material component for Arcane casters, or Divine Focus for Divine casters, but not all spells have this component difference. The other way to substitute a Divine Focus for a Material Component is if you have the False Focus feat, which specifically allows the use of a Divine Focus as a substitute for a Material Component of up to 100GP value when casting Arcane Spells only.
So the reason that the Inquisitor kit has both is because they need both to be able to cast all of their spells.