They are. The BLS puts together a 'market basket' that includes those items. However, it is the proportion that matters. Necessities like rent and healthcare ar

They are. The BLS puts together a 'market basket' that includes those items. However, it is the proportion that matters. Necessities like rent and healthcare are a larger proportions of expenses for the poor than they are for the middle and upper classes. When the market basket is created it takes consideration of everyone's expenses and so the weighting for healthcare costs say, falls below what it is that poor people spend on average and above what rich people spend on average (as a percent). Because these are a few of the spending categories that are inflating the fastest it is in this way that the CPI understates inflation for the poor and overstates it for the rich.