I'll second this, but I don't think it's a question of e-mail, more an issue of 'I'll deal with it later' coupled with indifference and inconsideration.
I interviewed at one company that said they'd be making a decision by the end of the week (it was Monday), and would let me know either way. The following Tuesday I sent an e-mail asking if they'd made their decision. A week later, I got an e-mail saying they'd 'gone in a different direction'.
Another company I interviewed with, which involved going to their tiny office miles from anywhere in the rain, talked to me for an hour about not really a whole lot, then said they'd let me know by the end of the week. I didn't care, since I didn't want to work with them, but I was very surprised when I got an e-mail a month and a bit later saying they weren't interested.
There are always exceptions though. After I left my second-to-last job, I decided to take a month off. My last day was October 31st, and I relaxed, cleaned the house, and played video games for most of November. When I woke up on the morning of December 1st, I had an e-mail on my phone from LinkedIn about a friend request from the founder of a server hosting company we'd worked with. I e-mailed him back and asked if he was hiring. Met him at 4 PM, and got the 'welcome aboard!' e-mail at 6:15.
It really comes down to culture. Some people have the attitude of 'I'll do it later', even for things that will only take a few minutes, and some people are go-getters who are eager to get things done and off their plates, and make some progress in the meantime.
My favourite though was when, in September 2008, I signed up to be put on a waiting list for a job at the 911 dispatch for the area (since they had just filled up their quota the week before). 18 months later, I got a phone call asking me to call them back as soon as possible (the tone in the person's voice implied 'today or early tomorrow') so we could schedule a time. The call went to voicemail, and I got something to laugh at when I got out of the movie.