phranque - 2:26 pm on Sep 12, 2012 (gmt 0)
you have both ExpiresDefault "now" and ExpiresDefault A259200 in directory context so i'm not sure which would override if it comes to that.
next i believe your regular expressions in the FilesMatch directives require a tilde (~) "operator".
otherwise it may be ignoring these contexts.
finally you should check that your subdomains are configured to properly supply mime types for these responses.
otherwise the ExpiresByType directive won't help you.