The market for 9 inch netbooks seems to come to an end in the foreseeable future. Customers choose the slightly heavier 10 inch devices because of ergonomics and comfort.
Asus Eee PC with 9 inch display: Will they phase out completely?
According to Digitimes the president of Asus' Asia-Pacific division Benson Lin said that in 2009 95% of Asus' shipment will consist of 10 inch devices. The remaining 5% will be 7 inch netbooks for telecom service operators.
The 10 inch displays are said to sell best. Currently some devices are offered with 9 inch displays but it is rather unlikely that further variants will be developed. The problem seems to be related to the 9 inch display itself. Although the display offers high resolutions, comfort suffers. Furthermore touch typing isn't really possible. The slightly higher weight of 10 inch netbooks doesn't seem to count as much for customers as comfort and ergonomics.