I think the slow is because it filled an empy niche. Once the niche was filled, like a flooded ditch, the sales rate slowed to match replacement/upgrade levels.
My wife just got one. 7 hours of battery life, a screen big enough to surf, a keyboard big enough to type 90%normal speed and small enough to fit in a cargo pocket. What is not to like?
My husband got one on a whim at the same time he bought a cheap laptop to replace a 5 year old one that was crashing on him. He liked the little one so well, especially for traveling, that it was a couple of months before he opened the box of the full size lap top. Months later he discovered that there was a 9 hour battery model, gave the old one to me, and got the 9 hour one. When we have traveled places where we will be on the go, these little computers are great. For example, we were in England last spring. The intercity trains had free wifi available. We could hop on the train and Freep as we traveled! We were also able to Skype with my daughter instead of paying expensive cell phone rates. Two fit easily in the space of one laptop in my husband’s computer case. I can also carry it around in my purse if I need to. The screen is smaller, so that can be an issue at times. We bought an external CD drive for software installations.