The first one is that the processor can't be that much of the total cost of a system. So these aren't going to be that much cheaper than a regular netbook unless they have a radical new form factor. If there is a new form factor, then it isn't really a netbook, is it?
The second is that it's all about software. Until we get to the point where everything is online, backward compatibility is still going to be very important and there are many things that people use that only run on windows. Or at least only on x86.