Fair enough. The instant on, instant to where you were, going from full screen app to full screen app features are said to use the SSD a lot. Instead of keeping all that stuff in RAM, they keep the info in SSD. Without an SSD (like with a hard drive) these switches will not be so instant.
At least that is what I read. If it is true, it also means that Lion will be very efficient with RAM, so Apple might not feel the need to offer 4GB as default.
What's the big deal? OEM RAM isn't that expensive. Take a look at the bestseller lists at Amazon etc. Find me a notebook that is more expensive than the MBA and has 2GB RAM or less. Or even half the price.
Only Ebenezer Scrooge would install less than 4GB in such a premium laptop product