Currently, most of notebook LCD panel, including those of our notebook, features a 16:10 format. According to Digitimes, 16:9 format should gain 10% per quarter in 2008 to become the default format next year.
The main reason might be driven by the ability of such LCD panel able to display full HD movie. But also for marketing interest, as it would allow to increase the size of the display in inches while not changing much of the true LCD area (in other words 17.1" with a display surface identical to 16:10 15")
So in a near future, we should see the MacBook Pro models to switch to 15.6", 17.1 or 18.4", while the MacBook could adopt 14" LCD.
[translation by Linathael]