Although Heathrow is only 40 miles away, it is a congested 40 miles by road and there are no direct trains.
Actually the run to Oxford from west London on the M40 is pretty good. The only real bottleneck is the High Wycombe 'pinch'. As for rail services, Chiltern Railways are planning to put a new link into Oxford from Bicester. There are also plans to upgrade the Great Western line from Paddington to Didcot and Oxford.
I would have thought radar would have taken priority over a runway extension. Still good news though.
Editted to add: They've got to sort out access to the terminal as well - its like driving on to an industrial estate.