For the World Wide Web to be truly worldwide, it must be accessible to all users, including those with low-tech equipment and those with disabilities. This isn't just being a good neighbor, it's also required by law under The Americans With Disabilities Act. Try turning off the graphics preference of your browser and see what happens.
Graphic buttons can render a page unnavigable and unintelligible.
A text-only alternative using the tag can supply the same information. A well-done alternative description can make content available for all users. Banners and bitmapped text look like type but are really individual graphic units which are unreadable by screen reader. And proprietary formats, such as major word processing programs require the user to have the same software to view them. Netscape's blink tag is more than just annoying to users of screen readers, it can make the blinking text disappear or even freeze speech systems.