$250 is not exceptionally low cost for a netbook. Furthermore the power dissipation of the chromebook under load is only slightly better than a comparable atom system [1]. The idle performance is better, I will give them that. Still, the death of x86 in the face of ARM for performance-sensitive environments (even when power consumption is a factor) has been greatly exaggerated.
[1] http://www.anandtech.com/show/6422/samsung-chromebook-xe303-...