Does your Focus achieve its 60MPG economy across the entire tank of fuel, consistently? Or is that a one off "if I do a long journey I can get up to" figure?
Petrol is currently considerably cheaper than diesel, and also emits less CO2 per gallon burnt than diesel. For your interest, our Prius averages 52MPG across the entire tank, day in, day out. If you account for the difference in fuel prices and CO2, your Focus needs to hit or exceed 60MPG on every tank to achieve the same.
You're also right in that diesels emit a huge amount more nitrous oxides and particulates, neither of which are very good for health, particularly in congested cities. As I see it, petrol has made great strides in catching up with diesel and reducing the benefits. Whereas diesel is perhaps running out of options and yet is still far dirtier and far less refined to drive. For example, the BMW 530i now hits just shy of 38MPG on the combined cycle, whereas the 530d is only 5MPG better at just shy of 43MPG.
Back on topic, I find it no surprise that Audi have canned their hybrid development - their entire range of cars seem pretty bad for efficiency when you compare them with their competition. You could view that as either they really don't care much about efficiency, or they have plenty of scope for improvement and catching up without needing to go hybrid yet.