Newly built houses are being forced to be extremely "green". Not only in the sense by adding extra insulation for roofs/walls and double-glazed windows, but a myraid of other stuff.
New houses built after 2016 need to be zero carbon (I know!) according to the UK Government. The houses are expected to produce their own power - geo-thermal heat pumps, PV panels, biomass CHPs etc. I agree, that's pretty over the top. But then again 2016 isn't that far away - and there are loads of trials on zero carbon houses.
These houses will be purpose-built for saving energy. Right from the roof to the foundations. Glass walls/partitions will be used to provide natural light, and not depend on electricity (at least during day-time). Likely to be close to air-tight; using mechanical ventillation and heat recovery (MVHR) systems will save further losses. All the electrical-stuff need to be highly efficient.
Old houses/flats can be renovated to some degree, but would not be practical due to costs.
Not all of us would be able to afford purpose-built energy efficient houses in the near future. So tearing down all the blocks and moving the people into "green" houses ain't gonna work...
Those flats and many many other houses will be around for ages. So you just need to find the right balance between the energy savings (in the long run) compared to the renovations that you are planning to do to save energy.