Apple sells to it with the 13" MBP, which you can get with 16GB RAM as a BTO upgrade. I doubt that many people opt for it, but it's not a non-existent market.
I didn't explain my point very well. What I was trying to say was how can "laptop manufacturers that refuse to offer the 16GB RAM upgrade option" (as izacus put it) be considered market segmentation (as AceJohnny2 said in his reply to izacus). It's not a segment to those that don't sell anything to them, and because they don't sell to them, they have no (first-hand) data on how big that segment might be if they were to sell to it.
I refuse to buy any laptop with less than 16GB of RAM.
Spent almost 1 year searching for a laptop to buy. Had to buy a 14" ASUS-RoG G46VW[0] and replace the screen for a 1920x1080 one.