Formatting/erasing encrypted partitions

This is more of a feature request. Where I work we have been using knoppix to shred drives using the shred utility for PC's that need to be decommissioned but lately we have begun to also encrypt the drives with safeboot.

If I want to reinstall windows on the drive I just use the Windows XP CD and delete the partitions that are encrypted and create a new one. However, qtparted and fdisk or cfdisk refuse to even see the partition/drive and allow me to blow away the partition and create a new one. I have had to resort to dban (http://dban.sourceforge.net/) since it has no problem with blowing away these encrypted drives/partitions. Why does linux care? Why won't it let me erase/format these partitions/drives?