I\'m in the trade of developing business web applications. They are mostly internal-use, sometimes with a partner zone, but rarely available to the public internet. They are
A big reason is accessibility. In a sufficiently big organization you will have a few users who need bigger text, screen readers, braille terminals or higher contrast. There are existing, well-established technologies for using those with "normal" web applications (if they don't rely too heavily on JavaScript usually).
Those technologies usually fall flat on their face as soon as your content is trapped in flash.