In addition to setting and action, there is a third type of start, which I think of as the "philosophical" start. It isn't that important to our discussions, simply because it's rare. I mention it for completeness.
Ever wonder what'd happen if everyone just stopped believing in money? After all, it's only worth something because people think it is. It's not food, which people need, or gold, which people like. It's just paper. Heck, for the most part it isn't even paper, it's just a record on some computer bank. Can't get more nothing than that. The whole world's economy runs on a shared illusion. It's totally Zen. Go figure. (Teen Inc., Petrucha)
I liked that book, but . . . that paragraph has no obvious connection to the rest of the book. I also rate the comment about gold as not true and the comment about Zen not true and probably out of character.
Many good authors have used this type of start, such as O'Henry, Dickens, Card, and King. And Crichton:
The late twentieth century has witnessed a scientific gold rush of astonishing proportions: the headlong and furious haste to commercialize genetic engineering.(Jurassic Park)
Like anything else, the philosophical musing probably would work better in the context of the story at the point where it's relevant. But it would tend to take the reader out of the story. Because the reader is not in the story at the start, perhaps that's the least disruptive place to be philosophical. However, I doubt that is why some starts are philosophical.
When the author is done with that philosophical start, the author still has to start the story, just like anyone else. It of course could be used to help (or at least cover up) an otherwise slow start.
The following philosophcal start is elegant. I once rated it one of my favorite starts, until I realized I liked it only after I read the book; on first reading, I was just going Why are you telling me this?, or really Who cares?
Things break all the time. Glass, and dishes, and fingernails. Cars and contracts and potato ships. You can break a record, a horse, a dollar. You can break the ice. There are coffee breaks and lunch breaks and prison breaks. Day breaks, waves break, voices break. Chains can be broken. So can silence, and fever. (Handle with Care, Picoult)
So, the basic bootstrapping problem isn't avoided: Philosophy can have trouble being meaningful without first knowing the story. (That book explores a family in which one child has easily-broken bones.)