I knew some clever clogs would say that. Well they become pedestrians again when they get off the bus ...
No seriously, they are two quite different concepts in transport terms.
Also, for any kind of modelling, the most "senior" type of transport tends to get the credit - so if you cycle to the station to catch a train, that's a train journey. Bus to station - train gets credit, and if you fly somewhere, well, you don't need me to tell you that one.
Transport bigwigs tend to forget just how important walking is in its own right. Every journey - from a trip to the shops to a honeymoon down-under, starts with a walk.
I might be a fully paid up lycra lout, but the fittest and slimmest people I know are the ones who walk. They don't just go to the closest shops, they walk across town or between towns / village and town or they walk across London. If they have to get on a bus, that defeats the whole point.
I know we're talking about a very exceptional case here, but Heathrow is a place of work as well as a transport hub. By definition, you should be able to walk into and out of it. I understand that there's a free shuttle bus, but that is still a failure on the walkability front.
The CTA may be a lost cause, but if a third runway is going to have any hope of being passed, there has to be a massive reduction in air pollution in the area around the airport, and this has to come through providing genuine improvements in the way the streets are configured. Also, this can't just be imposed on these areas, otherwise they will object to the measures meant to mitigate their objections!
It all has to be done through consultation and through best practice design, and this is why TfL are so key. That is perhaps the lost tragedy in them going on the "Boris Island" promotion tour. We all know the island airport is a regurgitated fantasy, but instead of making LHR R3 look positively rosy in comparison, it is drawing attention away from genuine mitigation methods.