曼昆 第496页有这样一段话：

The government includes this owner-occupied housing in GDP by estimating its rental value. That is, GDP is based on the assumption that the owner, in effect, pays rent to himself，so the rent is included both in his expenditure and in his income.

第497页有这样一段话：

Vegetables you buy at the grocery store are part of GDP; vegetables you grow in your garden are not.

自有自用的房屋要计算租金的形式计算进入GDP，那为什么自有自用的蔬菜不记入GDP？