(All right then, scroll down for content :-))
It is not necessary to quote an entire message when you are only replying to one specific part of it.
Minority? A mail client has been standard-ish for the last three to four years of upgrade iterations. There are a LOT of mobiles out there. Granted not many of them are used for e-mail, but that is a ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
One could say that "not many" is a reasonable definition of a minority. So, yes, a MINORITY of users have need for special message formatting. Why should the other 999 million of us need to change the way we do things?
Anyway, I wouldn't write a letter with nothing worth reading on the first page. I don't write articles with nothing in the first paragraph.
Nor do I, but there is a well-established tradition in written English of the preamble. One could say that a brief quote to set the the context of a statement is perfectly good practice. Of course some people take it to excess like the ones who wrote this declaration a couple of hundred or so years ago: We, therefore, the Representatives of the United States of America, in General Congress, Assembled, appealing to the Supreme Judge of the world for the rectitude of our intentions, do, in the Name, and by Authority of the good People of these Colonies, solemnly publish and declare, That these United Colonies are, and of Right ought to be Free and Independent States, that they are Absolved from all Allegiance to the British Crown, and that all political connection between them and the State of Great Britain, is and ought to be totally dissolved; and that as Free and Independent States, they have full Power to levy War, conclude Peace contract Alliances, establish Commerce, and to do all other Acts and Things which Independent States may of right do. --Michael Dillon