In supermarkets, they are. To most consumers, one brand of milk might as well be another brand--even if the tastes is different, it's slight enough to be negligible. So just shelving everything as 'milk' is good enough for the supermarket to handle is distribution duty. Now if one particular brand wants to do better than its competitor, it can pay for placement closer to the checkout section, or pay for a big promotional area for it.

The same might be true with apps. Yes apps have differences, but its not really clear that such differences are enough that there is clearly one app better suited for a purpose than another. Nor is it clear that you can both (a) divine the suitability of any app and (b) match that up with a consumer with any degree of accuracy versus alternatives.

If the above were true, central planning via the app store would be great. Since it's not... well our best known solution is capitalist market action which opening up the store to advertisement allows.