Might be just me, but I find having just one single 19" monitor keeps me more focused. It might be a psychological thing. When I had two monitors, I ended up having many things open at the same time and was distracted by the other screen. With just one screen, I could totally focus on the task, and I could quickly do alt-tab switching when checking programming reference API docs while coding.
Note also the trend toward for some people toward using ‘smaller’ screens, such as the growing number of designers and artists using their laptop as their main work machine. Nowadays, having a smaller laptop screen - say 13" or 14" might be preferable to a larger widescreen 15" model as it is more compact.
Screen size may very well be capped at the 22" limit for desktops and 14" for laptops. Bigger isn’t necessarily better.