I get the same impression. Maybe it's because every hooman on earth already has at least a 23" 1080p monitor, and the market is just saturated. Could it be that LCDs were much cheaper a few years ago, because everybody wanted to get rid of their big, fat CRT? If that is the reason, then maybe there will be more demand again when the first mainstream OLED enter the market.
EDIT: Come to think of it, another possible explanation might be that there are just less and less people who actually buy a PC and Monitor combo. Laptops and tablets are far more popular these days.
I'd wager the lower end monitors and the professional grade monitor sales are both going strong, but the market for monitors inbetween, like the gaming monitors, are seeing steady decline. Mostly for the reasons you listed and also the fact that more and more people are probably streaming their PC games to their TV. Why spend $1,000 on upgrading your monitor when you can put that money into a better TV and kill two birds with one stone.