By default, the only user-related item on the Places panel is the user's home folder itself.
This is a little sparse, and lacks typical locations like Desktop, Documents, etc. Most users will not take the time to populate the Places panel with more entries, so it's important to provide a more complete set of defaults. An especially useful one is Downloads, which will be heavily used in the Open panel given how frequently people download things from the internet that wind up there.
I opted not to include ~/movies because my sense is that most average users no longer have local video collections that they keep in their home folders, instead getting all of their videos from the web. ~/music is still there because enough people do still have local music collections.