I accepted naruto's answer above as it answered my questions, but also wanted to parse through the grammar that was confusing me.
The source of my confusion was that the active verb 限る is usually translated as "is limited to", a passive verb in English. (This discussion only concerns the intransitive 限る.)
A literal "translation" that is active and intransitive might be,
A has the limits that are B.
A is the agent, B is the indirect object.
A literal "translation" that is passive and intransitive might be,
B gives the limits, which affect A.
B is the agent, A is the entity that is affected.
These "translations" are not of much practical value (especially since passive, intransitive sentences don't exist in English), but are useful for understanding the grammar.
The takeaway from the accepted answer is that 限る、限られる、限られている roughly mean the same thing, and are all idiomatic expressions.