Only 10% of the devices are ldpi and this number is decreasing over time. Source: http://developer.android.com/about/dashboards/index.html
It is not required to have images for all the densities, only one is enough. The system will scale it up/down when needed. So the best approach is to have images for the highest density supported (xhdpi or xxhdpi).
I personally only use xhdpi images!