I tend to agree with the structure concept but that in itself creates other issues.
Let's look at a septic pump setup. Many of these units require 240v for the pump and 120v for the alarm. In some systems the alarm is tied to one leg of the pump-- problem-- yes. Since the 2008 we now have to have a dp breaker installed which would trip out the alarm on a short circuit or ground fault on the pump. Damn the alarm won't work. This makes this install illegal, at least around here.
Now run two circuits - a 240v circuit for the pump and a 120v circuit for the alarm. Problem again-- 225.30 unless one of the special conditions would apply (I didn't think it would). So if it's a structure, which I say yes to, then there is no legitimate way to wire the septic pump system.
I believe there must be an answer somewhere but as the NEC is written there isn't much that wouldn't qualify as a structure if it is detached from the building serving it. What is the intent-- who knows.