That is true, but Q4 starts in October and Apple will likely have access to early samples of the technology to allow them to bring the system to market earlier than most people. They have gotten first dibs on intel chips and chips from other manufacturers in the past such as the intel processor that was used in the original Air and the 8-core Clovertown chip that went in the first 8-core Mac Pro.
The Clovertown chip in particular became available in July 2007 but appeared in the Mac Pro much earlier, April 2007 to be specific.
Yes, Q4 starts in October, but given the information out regarding the LGA2011 and accompanying chipset series, an October release seems unlikely. So November or even December are more realistic targets (last I saw, Intel is trying to meet a November release - no week given, but as it's a rush, I prefer to be cautious and will figure for December).
As per early shipments to get systems out ahead of other vendors, that hasn't happened with the MP since 2009. The 2010 systems arrived later (~ 13 weeks after Intel's official launch of the Westmere's IIRC). The reason I suspect, is they just don't have the volume purchasing power for the MP's that they once did (pricing, probably, but not quantities sufficient enough for early shipments as well).
As per the board work, Foxconn has had access to ES versions of LGA2011, just like any other board maker in order to validate their PCB designs (Foxconn has been the ODM for the MP since 2009 systems). But even once they get the design completed, they still have to validate what's coming off of the assembly lines to be sure there wasn't a mistake between the final prototype (RTM design) and the production systems that roll out the door. This takes some time, particularly if there is a mistake (i.e. wrong part value for the PCB location sorts of things...). Once the assembly line output is verified to be correct, then they just need time to get systems assembled and accumulated to meet the first shipment.
If there's no major problems, the final assembly line validation + initial manufacturing run + shipping takes ~ 13 weeks on average. And this is the case for more than just systems; it's the same for components (assemblies down to discrete parts).
