Using Fivestar in Views causes the node update date to change

I'm not sure what you're saying.

If someone rates a node by using a Fivestar field on that node, then the node is being changed. The "last updated" time of the node should change every time the node is rated.

Is this not happening?

If this is intended, then in this case I will not be able to display only the materials updated by the admins on the main page. Fivestar creates spam from node updates as hundreds of users are constantly voting and rating nodes.

This is the way all entities with fields work in Drupal. Right? If a field is modified, any field, then by definition the entity containing that field has been modified, so the timestamp is updated for the entity. Fivestar isn't explicity updating the entity timestamp, that is being done by core Drupal.

Do you expect the entity timestamp to be updated only when the Body field is modified (for example in the case of a node)? How is Drupal supposed to know that you only want changes to some fields to be reflected in the timestamp, and not changes to other fields?