The example implementations of the hook_field_formatter_settings_* hooks (in field_ui.api.php) include conditions which check the field type.
I think it would be more appropriate if these examples used a check for the formatter type. The reasons for this are:
- The additional settings apply specifically to field formatters (not fields as such), but
- A field type can have more than one type of formatter, and
- Some field formatters can be used for more than one type of field.