P.G.
Generally, people update in the So What Happened so that everyone knows what happened. Usually, people don't respond to each individual responder. To do that, you click the name of the responder to send a message.
The people who answer usually don't expect a response. If a responder asks a question, it's usually to get more info for everyone, so if you want to "add" to your question, you can edit it - I usually put "ADD:" and then the new info so it's easy to see that more info was added after the question was posted the first time.