There's more than one thing going on here. As many other answers have noted, everyone gets more email than they want to have to deal with, and as a result there's a tendency toward minimizing as much as possible.
But there's another issue involved, and that's your (and their) communication style. The DiSC model for one overview, (search "DiSC" for many others) helps you recognize the issue and adjust your behavior accordingly.
Very briefly, the DiSC model says that people are either People focused or Task focused, and also either outgoing or reserved. Using those axes gives you a 2x2 matrix:
Task/Outgoing (D), People/Outgoing (i)
Task/Reserved (C), People/Reserved (S)
Everyone has all four styles available to them, but tends to naturally behave in one (or sometimes two) of them. Go read about DiSC for what the letters mean, and a whole lot more. For the purposes of email, people who are in each of the quadrants have different preferences for how they use email.
The high D will not use or expect a greeting, wants bullet points, bottom line up front (preferably in the subject line), tends not to use a signature block, and will appear very abrupt to an i or S.
The high i will tend to have an informal greeting using a name or nickname, a long signature block with every known means of reaching them, the message may be long, but don't expect that they'll read it all. A high i probably will not read an attachment, and is most likely to use emoticons.
The high S tends to use and want a formal greeting with a name, they appreciate a full background in the email, include more formal/traditional "how are you?" formats, and will close with a polite and formal ending and signature block.
The high C tends to see a greeting as unnecessary and wants all of the details in the email. Attachments are good when they have more supporting detail. A high C tends to use a simple signature block, with primary contact information.
The really cool thing about DiSC is that once you understand it, you can fairly easily change your behavior to be more effective with other people. If you are a high S communicating with a high D, you can make an extra effort to reduce the email you send to the minimum question and bullet points providing data, and not be hurt when they respond with asking how you are. If you are a high C communicating with a high i, you can remember to ask about their weekend, and make sure you get the most important information at the top of the email, expecting they won't read it all. (Note, technical populations skew more heavily toward high C and sometimes D than the general population. I see that in many of the other answers.)
DiSC is a powerful tool to help you work better with other people. What I see in your question is mismatched communication styles, complicated by the behavior many people have learned to be brief in their email.