"A threaded model eliminates this need and the confusion. A flat model would stiffle conversation here on PM."

Indeed. Just take a look at the IMDb message boards. They allow users to view threads in either flat or threaded modes. But the problem there is that when you sign up, your default view mode is flat. What happens is the newbies don't know (or care) to switch to threaded mode while the regulars eventually switch to threaded mode. You have half of the populution looking at conversations in context, and the other half viewing merely by chronolical order. I have seen, many many times, people getting into heated arguments simply because of this dual nature of viewing threads -- they think person A is talking to them when person A was really flaming person B. This has been going on for years, and people still get bitten by it. Despite numorous requests to make threaded mode the default, the IMDb site developers sill have not.

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)