The processor offloads the extra memory it needs to the hard disk. If you have an SSD drive, this is much faster than with a normal hard drive. Perhaps 4 gb wouldn't make as much difference as people think.
It wouldn't make a difference unless you regularly used applications that required a large amount of RAM. If you just use the Air for internet browsing, e-mail, and Office applications, and don't spend a lot of time with several applications running, you probably wouldn't notice.
I think we've reached the point where, technologically, more isn't always better. The computers on our desktop were unimaginable ten or twenty years ago, and the majority of users only use them for fairly basic tasks.
I would expect to see SSD standard in laptops within 2-3 years. With the release of some 512GB models, capacity is comparable with a hard disk. The prices should drop rapidly.
I remember almost twenty years ago, when I purchased an additional 4MB stick of RAM for my Mac. I believe it was several hundred dollars, and seemed almost luxurious to have that much memory available.
