I noticed that the database field types in comment_indexer don't match the fields in wp_comments. The most noticeable example is 'comment_author_url'. In wp_comments, the type is varchar(200), but in wp_site_comments, it is varchar(50). This means that urls are truncated. At first, I thought it might be performance related, but a lot of field types (e.g., comment_karma, comment_parent) are converted from int to varchar(255), which degrades performance. In the end, it just looks inconsistent rather than intentional.