1920x1200 is a 16:10 resolution, while 1920x1080 is a 16:9 one.
While for new TV's, as programs switch to 16:9, a 16:9 res makes sense, recently a lot of manufacturers are switching to 16:9 for monitors too, where it doesn't make sense at all, because while 4:3 is perfect for most work tasks and 16:10 can be fine, on screens from 19" up, for mixed leisure and work use, 16:9 means that you buy a new bigger screen and for some tasks, like word processing, you don't get any extra vertical space, and this sucks.
16:9 on PC monitors makes sense only for manufacturers, for the same diagonal, a 16:9 has smaller area and less pixels than a monitor with squarer aspect ratio, so, excluding old CRT's where widescreen costs more and has worse image quality, a 16:9 costs less to them (but not to us).