It defaults to reply to root if you click the root (in the header or footer) button (and is the only choice actually).
The problem with defaulting it to the root all the time is that then there will almost never be anyone that replies to a person specifically. I would challenge your assumption of "Most ppl are generally contributing to the conversation, to to one direction
person". Can you prove that, because I think the opposite is true (hence our current design).
Take this thread as an example. Sampy is the only one that replied to the "root". Everyone else replied to a person in the thread (and I believe that was their intentions).
It's a tough one to prove either way. You can't just go through the data, you have to read through each comment and verify what they really meant.
Ok point taken.
How about the ability to retrospectively alter whether it was a reply to poster or reply to root?
I think that would sort out the issue from most fronts.