Many, but not all things.
A couple examples:
We have a number of gas stations that offer lower prices for cash - if it's 6 cents less on a $3 price point, that's the same as the 2% reward.
A local dentist offers 5% off with cash (or check) vs. 2% for a credit card - cash still saves 1% even after rewards.
Not to mention the places that are still cash only. Or in smaller places asking an owner for a cash discount - they might just offer a deal.