You're comparing apples and oranges.

Shoplocket (I would guess) has a lot of users who are using it to sell retail items - which unlike app stores sales - have incremental costs as you sell more and more products. That 5% cuts into the margin of each item as opposed to an app that has a certain development cost and then no additional costs for increased sales (other than support + updates which would have to be done one way or another).

They're also not providing distribution, which Apple does.