[grafmax]

CPI is an aggregate measure which munges a bunch of things together under a single statistic.

In fact, the cost of necessities has overall risen faster than the cost of discretionary goods. This has been generally true since the mid-1990s; prior to that, inflation differences were much smaller across income groups despite lower income groups spending more of their income on necessities. In some periods like the post-COVID housing and energy price shocks, the differential effect of real inflation on basic necessities has been even greater.

Even "small" effects compound over time. For example, when someone in a low bracket loses 10% purchasing power after many years, the net economic stress they experience is much greater than for someone at a high bracket. Differential inflation of necessities vs discretionary goods magnifies this.