In his blog, Dana Blankenhorn raised a very good question
Do we need two open source office suites?
This is a very common question from people that still "don't get" OpenSource
While we could all be using the same tool for "compliance" reasons (that's why most of us use MS, isn't it?) there are many reasons not to.
Dana's argues that competition should only exist in the proprietary world. I disagree. In a commercial word it makes sense to make all the users use your tool thus the goal for each one is the less options the better. Knowledge sharing shrinks with competition.
In the open source world it's totally the opposite.
In the open source world, variety encourages innovation. Competition is just competition in a friendly way, where if your "competition" comes up with something awesome, you are free to grab it and include it in yours. Or study it and improve it. This is a two way street: knowledge sharing grows with competition.
What's more, successful projects have benefited from other projects that have flopped.
So, Answering the question:
Do we need two (or more) office suites, desktop environments, email clients, chat applications?
Of course we do not need them if we want to keep the "status quo", but they are invaluable to foster innovation, to try different things, and to help us realize that we are not all the same. Some people prefers A and some people B. And eventually people will realize that's OK.