This article makes the typical geek mistake of assuming that Android tablets are failing due to some technical reason such as "not enough apps". This assumes customers are making perfectly rational choices and are looking at things such as "app selection" when they "buy a tablet."
Right now there is not even a "tablet" market. There is an "iPad market." That is it. I was in the DFW airport with a friend. A bunch of non-Apple gizmos were on display in a locked case. One was a tablet. "What's that?" she asked. "It's a tablet." "What's that?" she asked. "It's like an iPad." "Oh."
People see tons of iPad commercials. They see iPads everywhere--in Starbucks, on the airplane, in the doctor's waiting room. The guy at work brings his in and talks about how great it is. All of them have that Apple logo on the back. No other tablet has this kind of dominance.
So people buy an iPad. They don't even know other models exist, and typically if you tell them there are alternatives, they don't care. The iPad is becoming synonymous with tablet, the same way iPod is the MP3 player and the Walkman was it back in its day.
Amazon may be able to overcome this with its marketing muscle. If they do, though, it won't be because they got some sort of "critical mass" behind Android to give it "more apps" and it certainly won't be due to geek crap like some sort of high-resolution screen or more gigahertz. A very low price would be a start.