fear of polarizing people
Businesses are not confident enough to polarize people on the web. They don't have enough esteem that the design will be sufficient enough to convert the target audience, so they want to design for everyone with hopes that the bigger net will catch more fish. The problem is that the design of the net itself gets in the way as it scales. The bigger net means a bigger frame and bigger threads which make it challenging to disguise the obvious nature of the device, thus resulting in fewer fish being duped into swimming into its grasp.
Making design assumptions without knowing the underlying human needs and context of use can be costly. Accessibility enthusiasts understand very little about the psychology of the web. I use the term enthusiasts for those that feel that all websites should be accessible by everyone. More and more the form and function are becoming tightly integrated, so that a change to one directly affects the other. Semantic markup, programming frameworks, and externalized style attributes are all a part of this movement. I take it a step further and say that everything boils down to design. Even words are designed to be read and there is actually an art to readable writing.
Designing one interface for everyone is a very noble and glorious in principle, but can't possibly be accomplished without some sort of divine intervention. Businesses today are afraid to polarize people. Cultural anthropological observations teach us self-evident maxims that people are different, and that humans have a natural tendency to self-organize into groups. Tribes have always existed and families have always existed within those tribes. And within those families, males and females formed subgroups where brothers did one thing and sisters did another. Page through the history books of any civilization and you will see gender roles clearly defined where men were expected to do one thing and women expected to do another. Gender roles have changed in modern society and have morphed and taken on various shapes, but they are still there.
The fact that men are typically stronger than women and naturally adapt to physical challenges better is a polarization of human beings created by nature.
Think about this. If we were to craft everything for all people, then the thousands of tribes that have existed over time would have been assimilated by now into a one world culture. The very nature of personas is the realization that the information-processing and decision-making needs of people vary greatly. There are universal values and universal character traits that persist in all humans. We all know someone that likes facts and figures for decisions. We also know someone that wants the previous person to shut up and give the big picture as it relates directly to their immediate need.
If you don't polarize people, people will polarize themselves. Think about all the cheap shots that PC users take at Mac users. Think about your restricted network of friends on myspace. Think about the devout Firefox users that went so far as to design a crop circle of the Firefox logo as a public demonstration of their loyalty for one web browser over another. Think about the bumper stickers of military moms.
There are underlying psychological factors for every instance of polarization and these factors are what should be used in implementing designs that address the core of the human experience.