Likewise, poorer customers are less able to avoid this kind of price discrimination at the grocery store.

If you walk or take the bus to the grocery store, you have fewer grocery stores to shop around for a deal at. If you're living paycheck to paycheck, you're less able to stock up on, say, cold medicine, when you see a good deal (and more likely to pay the "we know you're sick" price). And if you're time-poor (because you're working two jobs, and neither are the kind you can browse the Internet at while your code is compiling), you're less able to do comparison shopping, or notice that the price of what you need is always more expensive than when you don't.