If the power companies have seen the writing on the wall and expect a growth in microgeneration, perhaps to the point where it's the exception NOT to be microgenerating rather than the rule, then they could be attempting to build a long-term price differential between imported and exported power.
To sustain their revenues over time at levels like today, that price differential has to be around the size of the cost of imported KWh for a typical consumer (rather than microgenerator) today - and before the most recent round of 35% price rises - ie around 12p-15p/unit.
By their own argument (and allowing for investment payback time), imported electricity would eventually become - essentially - "free" aside from distribution and maintenence costs as generation companies reduce dependence on fossil fuels over time and shift to a larger use of renewables.
The rising price of oil/gas in the meantime will be used to justify more imported electricity price increases to a level high enough to comfortably provide that differential.
And then they can use the rising price of nuclear fuel rods... and so on and so on.
It'd be preferable, I think, for that differential to be set explicitly at a percentage and reviewed over time by a regulator. If imported power costs 20p/KWh, then exported should be bought for... well, any suggestions? 80% of 20p? 90%?