I'm not sure what your point is as, unlike Stafford, St Albans and Hatfield both get an overnight passenger service.
The point I was making (didn't see this reply until now) was it was 24 hour every single day of the week in St Albans except Saturday when people are out clubbing in London and would actually want to get home on a train.
As for why Stafford doesn't have such a service, it's either due to noise levels of the trains or a perceived lack of demand.