Large retailers use their equipment until support is no longer economical, which usually works out to a 7-10 year refresh cycle. With the much lower margins in grocery, that interval is even longer.

Retail terminals, even those with touch screens, are essentially communications nodes. The processing demands are fixed over time. Major OS upgrades or feature rollouts requiring equipment upgrades are extremely rare, so the terminals are usable for much longer than in an office environment. Although most of my current customers are using POS terminals with relatively current technology (P4 processors, USB peripherals), some of them are using equipment with design dates of 1998 (Pentium III!), simply because it still works and they can still get economical support.

On the other hand, prices for high-end POS terminals usually start at around $2000-2500 each, so this equipment definitely does not fall in the 'economy computer' category.