Uodate: iFixit have done the honours and have posted a tear-down of the latest MacBook Pro Retina - the RAM is indeed fixed to the motherboard.. and the display is such that it would require a completely replacement of the display assembly if anything inside it fails.. better get that AppleCare contract quick!
I have to say that Apple looks to have created a nice high-end workstation based on what was seen at the WWDC keynote yesterday.
But one thing troubles me. The lack of RAM expansion. While in the past you could always easily upgrade RAM in a MacBook or MacBook Pro – it doesn’t look to be the case.
The memory chips appear to be soldered to the motherboard – it doesn’t even look like they form part of a daughterboard. It looks to be the same for the flash storage too (although is that a screw by the right hand side of the flash storage block?). The MacBook Air apparently can have it’s flash storage upgraded (the stick of flash storage can be unscrewed and replaced and certain third parties can supply upgrades), but it’s difficult to ascertain from the above photo.
Therefore if you’re going to be buying one of these new machines, you’d had better pretty damn make sure you buy enough RAM for you to work comfortably for the next few years. You need to plan in advance on what you’re going to be using your new shiny MacBook Pro with Retina display for.
All that said I am, however, overjoyed that Apple have now set a minimum of 8Gb RAM for the basic Retina model – 4Gb doesn’t really cut the mustard much these days. The £160 to upgrade from 8Gb to 16Gb isn’t that bad (for previous generation, the cheapest you could do was £120 from third-party supplier Crucial Memory) – so it’s going to be worth your while buying as much RAM at the time of purchase than having to fork out for a completely brand new MacBook Pro down the road.
As there appears to be no user serviceable parts in the new machine, I’m guessing that Apple are looking to get more people on their AppleCare package. £280 gives you three years warranty. That logic board and all the memory isn’t going to be cheap if it breaks down outside the 1 year limited warranty included with the machine.
This new MacBook Pro Retina display is a gorgeous machine, but’s it’s going to need very deep pockets to be able to afford a specification that will last. That said – I’d still like one 
Until then, I’m perfectly happy with my mid-2011 16Gb 17″ MacBook Pro – now a potential collector’s item now that 17″ MBPs look to be discontinued.