The ISO paper sizes date back to the 18th century and are still used efficiently in most parts of the world today, showing that the system has stood the test of time!
The system is based on MATH—instead of Ronald Reagan's preferences—with each size having the same aspect ratio of 1:√2. This ratio makes it so that each ISO paper size is one half of the area of the next largest size.
Utilizing the ISO 216 paper sizes will thwart confusion between designers and printers, as well as help laypersons when making posters and flyers for garage sales and stuff.
Read more about ISO 216 on Wikipedia, The Free Encyclopedia: http://en.wikipedia.org/wiki/ISO_paper_sizes