Wasn't it rumoured that the entry level cards would come first and the mid-range to high-end would come at some point in 2011?
Yeah.
4Gamer.net posted that roadmap a while back that showed the Cedar and Redwood replacements launching in the time frame this and other recent articles have spoken about. The article mentions the Juniper and Cypress replacements will have the most improvement in performance, so it would make sense to launch them later to maximize 5700/5800 sales before they are phased out.
That all said, product series usually launch from the top-end down. There's been mumblings elsewhere the high-end is launching first, and of course we have that quote from the HIS guy about reference products launching Q4 with AIB-designs in Q111, which is a hint at weak initial availability.
Elsewhere people have claimed the second tape-out was sent to the fab in mid-to-late July, which with the 3-month avg turn-around rate would mean a launch in October/Nov with scarce availability, which again meshes with this report. Furthermore, if the SI series was designed like Cypress/Juniper, or perhaps even more coordinated (if half of Cayman is Barts, half of Barts is Turks) then a bug in the design (which the rumored second tape-out would infer) could delay the whole series. It's possible that had the first tape-out had been a success, the series' launch would have been staggered in such a way as that road map suggests, but now they are launching closer together.
It's also possible the ridiculously low pricing from nVIDIA caused them to rethink their strategy going into the Holiday season; launching with lower availability (or paper launches as this articles infers) on the higher-end parts. If they offer more performance per mm than Evergreen, this would make sense more than ONLY slashing prices on the 5000 series and riding it out until early next year.