The 20GB, 40GB and 60GB versions of the PS3 have been discontinued. According to this, it looks like the 80GB PLAYSTATION 3 is next.
This notice is apparently from retailer 7-Eleven (7-Eleven sells video games in Japan) and states that pre-orders for the Black, White and Silver 80GB PS3 will cease on Sunday, August 9 at 10am.
The reason listed is literally "For the manufacturer" — or at the maker's request.
The notice also notes that all in-store displays for the 80GB model are to be taken down. If this is true, then Japan would be left with possibly the not-sold-in-Japan-yet 160GB PLAYSTATION... Or perhaps there is an upgrade in store...