A DPF's lifespan is governed by driving style, vehicle maintenance, etc and cannot be quantified as 'they go at 70k', etc. As an example, my parents have bought a Focus with a DPF, against my advice as I knew it wouldnt suit his driving style. They bought the car with 85k on it, original DPF in place, after 3 months it went back for a new DPF under warranty as it had completely failed. 5 months and 2k miles later it has failed again. It is presently at my mates garage having the DPF bypassed and mapped out.
The reasons behind it are that the car does 3 miles to work and 3 miles back 6 days a week, then will do another 3 or 4 miles every day in a separate journey to visit my Gran. In that 5 month period it has made a couple of 90 mile round trips to the Metro Centre, never at high revs and when the DPF tried to regen he stopped the car because he thought there was something wrong with it despite me warning him that it would happen. He shouldnt be driving a diesel and certainly shouldnt have one with a DPF.
In other words, if it is looked after it will last (Y)