Now fast forward to modern day, and the cost/time required to send an email is trivial. More emails get sent. Busy people get more inbound. Social conventions obligate you to respond, especially if it's someone you know.
We'd all be better off if the expectations of response were lower. That's why I like Twitter. There is little expectation or obligation to respond.
Of course, being a largely useless college student, I hardly get inundated with emails and so will probably respond in either case, but I would certainly feel better about ignoring an email than ignoring a letter.
In my experience, the math then works out that numerous people are still angry if you don't respond to their e-mail; I have had people make entire blog posts about how horrible and dishonorable I am for not responding to e-mails that didn't even have any concrete questions or action items.
On the far end of this is Twitter: I get tons of messages on Twitter; enough that, when something is "happening" in the iPhone ecosystem, I have gotten hundreds of @replies in a few hours (in slow times, I thankfully get very few). However, Twitter only lets you get 800 messages from any non-timeline search, even using their website.
This means that if I'm not sitting around checking Twitter all day, there is no way I can even see all of the messages being sent at me, much less respond to them. However, in all of that mess, there are at least a few people who get really angry that I didn't see their message and respond to it personally.
Once, I spent a couple weeks, spending nearly all of my time answering e-mail. I still had people get really angry at me for not responding to their messages, and I now also had people angry at me that I wasn't accomplishing anything (such as writing new code).
Additionally, I was now getting much more e-mail, as the people I was responding to were taking that as an indication that they should send me more e-mail. That experience made me question the value of responding to anything at all. :(
(Sometimes I fail to resist the urge to respond, as you can see.)
But writing like a dinosaur, with short well thought-out responses. Now that doesn't take that long. And you can see this in how prolific @FAKEGRIMLOCK is.
To put it another way: LONG RESPONSE TAKE TIME. TO THE POINT. QUICK.
As Pascal once said, "I apologize that this letter is so long - I lacked the time to make it short."
But then you start rambling. Because rambling is easier than Just Saying What You Want (tm).
What you actually convey is not.
"Omit needless words."
The trend in our ability to address those outside of our immediate social networks seems to be that it will only get easier as time passes. Either our idea of what constitutes polite social reciprocity will have to change, or new ways of mediating these communications will have to be found (automated prioritizing, etc).
Today, E.B.White would just set up an auto-reply and get on with his next book.
ETA: Right, he wouldn't as indicated. Though something would give, and some technology would be leveraged, making replies take much less than hand-typed-on-paper.
I disagree. In fact, White himself disagrees in the letter. He could have set up an auto-reply by letting his publisher handle his mail, but found that "evasive and unsatisfying".
What's worse, "thank you" emails also socially force me to add mere "be nice boilerplate" to mu future emails to that person, instead being short and to the point. It's funny how technical, business, or fact based conversation can become unnecessary long and loose the focus with all that boilerplate.
On the other hand, being nice and polite is good in real life, on the face to face (or voice to voice) conversation, but, IMHO, just waste everyone time in email.
I rarely hear back, and it acts as a filter for those who are willing to put in some effort.
Support email is my enemy.
I have read about successful people who do the same.