To me the emphasis is simply an implication that their customers get pitched a lot of programs where the payout has strings attached. (A common tactic to exploit the poor- see the old "company store" days)

Simple example, the reward points I get on my credit card are not cash. They can be redeemed on my mortgage, but not on shoes.

A product that is trying to differentiate itself from such programs would certainly want to really emphasize that they are giving you cash.