Maybe 600 series is an OEM only line for their fixed refresh period like the HD8000 series that came just before/alongside the R 200 series? OEMs just want cards with bigger numbers than before and ready for the summer refreshes.
If you think about it, it's not bad news if the rx630 is a masked rx470/570 for about 100$ and the 640 is a rx480/580 for 120$ to 140$... Still great value for money...
