"Save Settings" only applies to the survey selected in the "Survey" filter at the top of the page. If this is chosen, it will create custom report settings for that survey only. Once this is done, any "Default" report options will not affect that survey.
"Save as Default" will only save those settings for surveys that have not already had settings saved. If the "Options" have been opened for a survey and the "Save Settings" button has been chosen, the "Save as Default" will not affect settings for that particular survey. The dialog box that comes up when "Save as Default" is clicked explains this:
"Are you sure you want to save the options on this page as the default settings for ALL surveys?"
Note: This only applies to new surveys and existing surveys for which no report settings have been saved.
If the "Save as Default" or "Save Settings" buttons did not work in the way described above, every time "Save as Default" is clicked it will overwrite the report options for individual surveys, which makes the ability to save specific options at the survey level useless.
This is very important to know: By selecting "Show All" from the survey list, only the "Save as Default" button will appear at the top of the Options page. The "Save Settings" button will not appear because the system doesn't know the specific survey that the individual settings are for. It will look like the options were saved for all surveys, but if a survey already has specific settings saved; those settings will not affect them.