Attachment viewer?

Why does the attachment viewer not work for files that are on the media card? It clearly can open the file format and we can navigate to the files via the file explorer. What is the holdup? I understand that docs to go will be a welcome addition when offered, but I don't know why there are limits on software that is already installed when files can be navagated to and the formats are supported. The attachment viewer can open docs, xls, jpeg, ppt, and pdf formats; it would be nice if those existing capibilities were available to all files.