Yes you are. First, you misrepresent the weight differences. Then you say there is no intelligent reason for buying one, implying that those who bought one are stupid and have bought into the hype.
As I was queuing at the till at a nearby department store to buy some blank DVDs recently, I watched someone buy one at a nearby department store. They were a reasonably well-off middle aged couple, judging by their appearance, and they were taken by its size and weight. This thing slips easily into a briefcase or other light bag.
I used to carry around my BlackBook and even that got annoying after a day of carrying it around a busy city in a single-handed carry case, getting on and off trains while also carrying work and also my bag... and it was overkill for that purpose. For those who have the money, the MBA makes a perfect secondary computer or netbook. People don't necessarily buy on tech specs alone and they have their own entirely valid reasons for doing so.