Incentive offers usually have a lower payout than non-incentive offers.
Because you're getting conversions by giving something to the user in return. For example, I'll let you watch my super cool video, if you download this app. Or you'll earn more lives in my game, if you answer this survey and submit your email with it!
It's a reward given so as to lure and acquire users!
Non-incent offers tend to acquire more loyal users, though.
Because these people are really into the product that's being advertised. They like it, and don't need an incentive to do so.
There was something on the banner (or whatever promotion form) that got the user's attention. That's why they went and acquired the product, motivated by their own will. At the end of the day, these driven users will make you more profitable as an affiliate marketer.
Can you promote incent offers without having something to give away in return? I think so. Nonetheless, if you have the same product in a non-incent version, go for that one! Always!