What do you mean by "rare"? You just click "order". It's not like you have to go on the quest for the lost arc or anything like that. They are uncommon in the sense that people don't actually get them, but that's not because of a lack of availability. People do not want them.

They mean the models are rare, not the devices. The claim is if you want feature X + removable battery, it's unlikely that you will find it. People's willingness to forgo the battery for feature X therefore doesn't tell you if people care about removable batteries in an absolute sense, just that they care relatively less than they do about feature X.

You could argue that the market already reflects people's desires via, eg., Apple's market research. They could argue that democracy in the EU also reflects people's desires.