They exist, but they are hidden from the masses because they don't care about this. If they are not hidden to the masses and the masses are not guided you get a chaotic mess of confusement, or people with too much time figuring out what is best for them.
So instead of having an ICQ Messenger, an AIM Messenger, an MSN Messenger, IRC chat, Yahoo Chat you have by default Pidgin and it does all of that reasonably well. If I install Ubuntu Desktop I get Pidgin. Maybe I'd like a dialog when I install Windows, to ask me if I want Mozilla Firefox, Opera or Microsoft Internet Explorer. I wouldn't pick the latter then, and at the very least I want the choice to have applications use something else than MSIE or Trident to render their stuff. And instead of having 100 choices you need to make clear to the customer why your product is better. For example because it contains less fat, or because it has some official label, or some random buzzword.