This used to be fairly common when the estate tax exemption was low. Now that it's pushing $7M per person and temporarily doubled, a married couple can shelter around $27 million from estate taxes. A much smaller percentage of the population even need to think about the estate tax now, so you don't see this happening very often any more. Very few people have any incentive to try to manipulate values of their parents' estate because so few estates are even subject to the estate tax now.

I'm guessing that the fact that the house was worth $12M is an indicator that the deceased individual has a taxable estate.