You would only put the exclusions in High + Default if -
a) You wanted to
b) You were not sure which of the two profiles need the exclusion
It would not be a "best practice" to put the exclusion in both profiles unless it was needed in both profiles.
Thank You Warren
But still I wait to get an update from someone who did similar exclusions (for AD / Exchange 2010 / SQL / Sharepoint etc) and eager to know whether they did the exclusions with both high & default profiles