Where I come from, threads did that every 3 posts deep. Or rather, if it hadn't by then, it was unusual.
(Keeping in mind that it had a tree-structure: so 10 replies to the original is still only 1 post deep)

Does anyone use Outline or 'Linear+'? I've never understood them.

Outline is the "tree view" although this board's implementation is shitty.

Linear+ is exactly like standard, except the original post is always at the top of each page.

Yeah, the tree is always flat, so there's no point.

Hm. Keeping the OP on the top would only distract from the digression, though.

Almost, simply because we're used to a linear conversational flow. But if you check this thread you'll see it actually does go 2-deep in some places.

I assumed it was because I see no way to Reply to anything other than the bottom. What button does it?

Quote post.

Ah. I've never used that, because there's the quote tag. Makes sense, but I would've expected a ReplyPost button. Anyway, good times.

Many native English speakers lack the idea when it is OK to say 'fuck' too, and just say it all the time

*just watches the thread completely derail, killing hundreds*