I looked at an upgrade for my 64GB drive, and the 180GB upgrade is intriguing, but not at nearly $500. Not in my "still unemployed" budget, unfortunately. The upgrade is laughably simple. You're spot-on with your guess at how many will be sold. That largest SSD along is more than I paid for the entire MacBookAir. Sheesh.
"Not everything that can be counted counts, and not everything that counts can be counted." Albert Einstein