I understand and agree with the fact that user avatars are not returned by default for trackbacks and pingbacks by default. However, it would seem to be a bug or at least very undesirable behavior for the get_avatar filter(s) to not be applied. We are all counting on WordPress apply_filters being called when its supposed to be.
from version 2.8.4 pluggable.php:[code]
if ( isset($id_or_email->comment_type) && '' != $id_or_email->comment_type && 'comment' != $id_or_email->comment_type )
return false; // No avatar for pingbacks or trackbacks
... a whole lot more code here that doesn't always get called
return apply_filters('get_avatar', $avatar, $id_or_email, $size, $default, $alt);
So obviously I can fix this, but I sure don't want to start modifying the core WordPress code. That's the whole reason for using/writing plugins in the first place ;-)