I believe the area shown on the plan above to the west is just the new sliproad and infrastructure from the M25. This is an old plan that shows T5 as 'under construction'.
Regarding T2 etc. the whole of LHR is currently being redeveloped so that the airport is laid out parallel to the runways rather than the hexagonal design from the 50's. You can see this in the way both T5 & T2 have been designed and further taxiway improvements are/will be done also.
Lets be sensible here, people want to fly into Heathrow, yes everyone complains that it is a dump but that is exactly the reason it is being redeveloped. T5 & T2 are impressive terminals despite the typical British trait of trying to find fault in our own achievements. An expanded LHR could be a great asset to the country. It will help us build our way out of the recession and will be mostly financed privately, it seems like a win/win situation to me.
As has been said this is more than just an airport, the associated businesses and infrastructure as well as all the workers can not just be relocated to Kent. This is something that Boris fails to mention. He will talk about new jobs around the Thames Estuary but will not speak about the affect of closing LHR on the west of London. Many of the nimbies in these areas do not realise what affect this will have on their surrounding areas but it will have a huge affect on west London and the Thames corridor.
I believe what we are seeing now is the political wheel turning round to what was always going to be the inevitable conclusion, LHR expansion. The cost to the taxpayer both direct and indirect of these political games is what we should be complaining about. This has not been about finding out what is best for the UK but about getting in power and saving face.