The W510 uses the Clover Trail processor which is a 32 bit processor and the maximum amount of memory a 32 bit processor can address is 2gb. So it's a limitation to all the Clover Trail systems. You would need a system like the W700 which uses a 64 bit processor to address memory beyond 2gb.
a) RAM memory is hardwired, there are no slots. Same may be true for SSD. From Intel "Includes support for LPDDR2 800 MT/s data rates, up to 2 GB." What exactly this means I cannot say but the limit for 32 bit addressing is 4GB. It is possible that Intel could not meet battery life requirements with 4GB.
Or it might just be marketting - to get 4 GB you have to move up to the $700 class of tablets which are more "notebooks in a box" than tablets. That is a niche that "Bay Trail" is supposed to fill.
Personally I expect a new class of 7" Windows tablets based on Clover Trail to appear about the time that 10-11" "Bay Trail" tablets and ultrabooks appear.
Once you stop thinking of "tablet" and start on "multifunction personal device with docking stations" then the need is for somethig that will fit in a jacket pocket or purse and in a double-DIN dashboard dock then the case for a 7" screen becomes obvious.
Yes, CJF is touting an 8.4" automotive unit but when you look closely, that is a 7" screen with soft buttons on top and bottom.
Right now I am working with a W510 based "office" that includes a special "dock" (we really need a standard docking connector), keyboard, mouse, 24" monitor at 1920x1080, RJ45, and 120GB partitioned SSD running WTG. In the car it adds DVD (SD based music/video), GPS, rear camera, and powertrain/fault monitoring. Out of the "dock" it is a plain W510 with all normal capabilities.
Is somewhat of a kludge right now since no car charger exists (yet) so need to use a second power supply and a 180W inverter in the car and both require powered hubs but the capability is what is important not the form factor.
So if you need 4GB of RAM either buy an I3/I5 tablet or wait for Bay Trail. My focus is on a 7' unit.