It is worth noting that some cars do general tend to wear unevenly anyway. Quite commonly, negative camber on german cars causes the rears to wear on the insides, and positive camber up front causes wear on the outside. Supposed to be better for high speed cornering apparently.
Additionally, all tyres are not the same. Sometimes different brand/type replacement tyres will wear differently to OEM tyres as some tyres will be wider/narrower than others.
Having said all that, the biggest cause in the UK is town driving. Potholes will knock off the alignment.