It is the sad fact that in our current society (mostly) only closed source softwares are used (and taught) in schools - at least in the US. This fact, combined with the resistance to change that is inherit to most people, means people are more inclined to click on that big blue E when going to surf the Internet as opposed to my favorite fox. Many users simply use the software that comes pre-installed on their computer or what is recommended by the sale's person. For example Microsoft Office.
In many FOSS vs Closed Source project comparisons I have seen to date this "user familiarity" is often referenced as a point of "software superiority". Not only is this a flawed form of logic, but it is really borderline FUD. The familiarity the users have with a given piece software is not something that they where born with (or was even developed over night). It is something they learned over an (often extended) period of time.
Do you think a time will ever come when users will realize that just because you know how to use a piece of software doesn't automatically make it the best software for completing the task at hand?