It's a typical 'non-joined' up transport policy. The idea of the 'Boris Island' airport is sound but only if it has a ground infrastructure enabling it to serve place such as (mentioned elsewhere) the M4 corridor, with reliable, fast, frequent and moderately priced direct rail services.
I still maintain that Birmingham is the best of all the UK's current airports for expansion into a real hub. Not ideal, by any means, but the least bad.