You're not misinformed.

There are other reasons someone might have alts*, but needing to do so in order to play as a different class isn't one of them.

*Friends on multiple servers, enjoying playing as more than one race, seeing the other nations' pre-15 stories, getting around weekly caps on tomes (this is only a concern for level capped characters), extra storage if you can get a friend to pass things back and forth or have access to the same FC chest, the heck of it, etc.