Netbooks with larger displays tend to have larger keyboards, which makes them easier to type on. So while there’s no actual difference in screen resolution between netbooks with 9 inch displays and those with 10 inch screens (both tend to have 1024 x 600 pixel displays, give or take a few pixels), the larger models may be easier for some people to use.
Asus expects 95% of its netbook shipments in 2010 to be 10 inch Eee PC models. The other 5% will be netbooks with 7 inch screens. Those smaller netbooks will probably sold through telephone companies.