My more than 47 words reply
Having a real email client open 24/7? Yes, I do and it is set to get emails off the various servers every 15 minutes. I do not have a cell phone and I rarely give out my phone number, email is the best and most preferred way to get in contact with me. Response time varies depending on who sends me a message. Some I can and need to reply right away, but most sit there for a few days and plenty of messages do not end in a response. If there is no request for comment I do not see why I should give my 2 cents. That is my reason why a good chunk of emails are left unresponded to. Another reason is that I often get several emails from the same person. I tend to respond to all those messages in one response, but not if it is for business because there it does not help merging threads. If I want to boil an egg I get up and do that. I reserve the right to be not available for hours. Put that in your pipe you smartphone hogging folks!
Short responses...yes, but it depends who I am conversing with. I know of SMS, but SMS is by far more expensive than email and there are no free SMS services for desktop. See above, I refuse to spend hundreds each month on a data plan for a smartphone, too expensive of a toy. I do appreciate and typically add a proper thank you and address, but especially at work with mile long email threads I think we can do without it. We all know that we each appreciate the others contributions, but there are better ways to express that than a reply to all "Thanks! Have a great weekend!"....especially when it is early on a Thursday! Cutting out the niceties is not a matter of disrespect and lack of appreciation, it just keeps the email volume down. As nice as a 'thank you' is there is no additional information conveyed by it. If you think I did a great job send a note to my boss.
Most of my responses are more 47k words long. I constantly get dinged for not being concise enough. Others who email me are very concise and I constantly have to email them back to give me more details and above all context. Maybe it is just because I am old? Nah! It is because I know that others have gazillion things going on and it would be rather obnoxious to assume that they know what I am talking about when I write "I disagree with 2.1, it should be moved to its own dialog or be its own tab." So I add more context, but often get a response "Agreed!". Great that you agree with me, but to what? The dialog or the tab proposal? Being concise is fine as long as the response still contains information rather than just data.
Kids are smart, email has so many benefits that are not matched by any other communication platform. And you can attach or (although I hate it) embed content other than text. Try that with SMS or tweets.
Email will be around and do well for a long time. It is easy to use, very versatile, very easy to index and search, very simple to pass on to others, easy to archive, and above all accessible from almost any platform and dirt cheap.