It's just about the right amount of space to have 3 windows open, one in the center and on each side. That's about how much content I want to have on screen at once, anyway; more quickly hits diminishing returns. You could go for a slightly larger monitor (this is personal preference), but too much larger will out the side windows at an uncomfortable angle relative to your keyboard and mouse, which can lead to neck issues.
You can approximate it with three vertically-orientated monitors, but the gaps between screens reduce layout flexibility and are not good for multimedia. So you'll end up pulling the center monitor forward and changing to landscape when you want to watch videos or play games. Also a triple monitor setup is just a lot more to set up and deal with -- cables, stands, desk space, etc.
I agree, but it seems like there's and (unwelcome to me) industry-wide trend towards less density and wasted screen real estate. At least Apple still ships 16:10 displays, unlike the 16:9 garbage that's ubiquitous nowadays.