You'd be surprised. We did our study in the suburbs of Canberra and found elevated levels in lots of the homes we tested. Not enough to be a health risk in the places we looked, but more than youd expect all the same. Its mainly geology though. You don't have to be quite a uranium deposit, but if the geology in your area is the right (wrong?) type then you'll find it.
Ahh the days of being a graduate uni student door knocking in the suburbs asking people if you could put a radiation testing device in their kitchen :) I don't miss those at all !