No mention of it being a cylinder-on-demand petrol engine - that would have improved the real mpg in petrol mode by a very real 10mpg or so.
If you want to be doing the equivalent of 180mpg or thereabouts, you'd probably have to be having it in 100% electric mode for 70-80% of the time. In fact, the CO2 level of 35g CO2/km suggests that at around a quarter of the petrol model's own figures, the official cycle has this car working in electric mode for around 75% of the time.
Fine if you want to drive like a nun while doing a 30 mile round trip commute - you might hardly have to dip into the petrol side of things. Who wants 204ps on tap, knowing full well that they can only tap into a quarter of it if they want to get appreciably getter mpg than the GTD? It'll likely cost £9k more than a GTI/GTD (their "estimate" seems wildly optimistic when you see that the e-tron has a confirmed price of £34950 after subsidy - albeit with more equipment than is usually standard for an audi), or £4k after the £5k current government subsidy (funny how all these electric cars are around £5k more than they should be while that is in place. If the subsidy got pulled, they'd find a way to reduce the price so it didn't look ridiculously expensive).
£4k can buy you a lot of diesel in a typical 3 year ownership of the car, enough to do 33k miles at 50mpg (assuming current diesel prices of £6 a gallon/131p/L). Even if you are getting your electricity for free (free charging point at work?) I can't see why you'd pay the extra for the GTE over the GTD.
This car makes perfect sense in London to avoid the congestion charge, but outside London you'd be better off with a GTD when all you are trying to offset the extra cost with is fuel savings. The extra weight of the battery pack blunts the all-in GTE performance to worse than that of a GTD (just).
If you have a strong environmental conscience or you live in London you might be swayed, but if not and you only intend on keeping the car 3 years, you'd be better off with a GTD from a financial point of view, while these come at such a premium.