One way to see that this is different from a 7% return is to ask what happens if you wait 2 years instead. A 7% return on $1000 invested for 2 years is $1144.90. If you let $1000 earn 5% for two years, you have $1102.50. With 2% cash back, you can then buy $1125 worth of stuff. Not the same amount.
Now try 30 years, and the difference is between $7612.26 and $4410.15. Definitely not the same.