Actually...the area difference is not a small reason why companies are going toward widescreen. It results in better use of the mother substrates that the LCD panels are cut from.
For example, your typical 5th generation substrate measures 1100 mm x 1300 mm...if you make traditional 19" (5:4) monitors, you end up only able to fit 9 such panels on each substrate. But if you make those newfangled 19"W (16:10) monitors, you can magically fit 12 such panels on each substrate (try fitting the panels in, you'll see what I mean), thus getting three more panels for basically the same amount of work, and can advertise them as 19".
Now there's talking of doing 18.4"W (16:9) panels. Why? It allows you to fit an 24 panels per 6th generation substrate (1500 mm x 1850 mm), compared with 20 panels for a 19"W (16:10) panel on the same substrate. The recent development in weird sizes, such as 15.6", also stem from the same reason. A 5th generation substrate can be cut into 15 15.4"W (16:10) panels. But if you use 15.6"W (16:9), from the same substrate, you can squeeze 18 panels in, and advertise a higher size to boot (the area is about the same for both).
Basically the reason for the sizes that you see are due to the sizes of the mother substrates that the LCD panel manufacturers chose when they built the factories. Why did we jump from 17" to 19", with no 18" in between? Because it's not cost effective to make panels in the 18" range, as there'll be a lot of unused (hence wasted) real estate on each substrate if that size is chosen. Hence, before the widescreen trend, it was either make 12 17" panels or 9 19" panels from a 5th generation substrate; an 18" panel would've been too big to fit 12 panels per substrate, yet result in a lot of wasted space if fitting 9 panels per substrate, so (mostly) no 18" monitors.