Yeah a thread is more like a close conversation. If you comment in a thread you're going to be heard front and centre. It keeps non-sequiters down and it's good etiquette to at least acknowledge the points raised above.

Tree based is more like splintered conversations around a party, where people drift in and out of side convos. This lends itself to a more anonymous, transient communication style.

Ideal for a quick little session on your phone, really