Recently Google confirmed that they are retiring Adsense for domain (parked hosted domain) within Adsense. They are no longer serving hosted domain and they are not accepting for serving adsense ads for new domains from 22 feb for new publishers.
After 30 days existing publishers also not able to create adsense ads for new hosted domains. From 18th April all existing hosted domain will be inactive and can not earn from there hosted domains. And most probably from june 2012 this service will be disappear from all adsense accounts.
Those publishers parked their domain and serving adsense ads for domains they need to change name nameserver and DNS setting before june 2012. You can know more about retiring adsense for domains from here.