It's one of D2's secrets, one to be revealed as D2 grows and expands through dlcs. In other words, some random npc will make a one sentence remark about it somewhere in the third expansion but you won't be able to get to that point until you've paid for the first two and then bought and played through the third. Of course, you would still have to find that one random scan-able item in the dark, obscure corner of Io where noone would ever think to look. :P