They could have gotten the conversation right when they introduced the quote system (put a link to the tweet you are responding to and the client/site will embed the tweet body inside yours), but instead managed to break the existing system they had where a client could include a tweet id number to indicate what tweet someone was replying to when using @username.

End result is that rather than have the potential to build a conversation chain, readers have to manually drill the "tree".

Never mind that they never implemented support for merged SMS (introduced all the way back in the 90s!), so you are constantly stuck at 140 characters.

All in all it is a quintessential US company with the classic US mobile network blinders firmly fitted.