Desktops I build with current generation parts once every few years... laptops, on the other hand... I buy second-hand business laptops that are 2-3 years old, and save gobs of cash on quality products. I briefly thought you were off mark on large laptop screens being uncommon, but I'm having trouble finding ANY > 17" that aren't overpriced gaming laptops... that being said, I'm writing this on a 23" 16:9 monitor, and I actually feel like a 21" machine wouldn't be all that insane for a desktop replacement machine, especially if they minimized the bezel.
edit: I see now that someone replied to you with an absolutely ridiculous 21" gaming laptop xD ... I purchased my current car (used Crown Victoria, with only 11K miles on it) for as much as that thing costs.