I thought "wait, hasn't that been released yet?", looked it up and it's the "R2 FR/NL" release I was thinking of... ;-P
I think that When They Cry was released during a period where many more anime fans shopped by cover art at Brick & Mortar stores. I think that nowadays with anime fans being more internet savvy (and shopping at RightStuf) When They Cry would fly of the shelves. I certainly have heard a lot of buzz about it over the last couple of years.
I thought it was "lots of online buzz about Higurashi -> anime gets licensed and released -> too few people creating online buzz about it actually spend money on the DVDs"...
AKA: hype != sales