IANAY (I am not a yank) but didn't JC Penny backtrack on their idea to stop having promotions, but constant low price?
websites like hotukdeals constantly show how people will buy pointless things they never wanted, because they are 'cheap', then moan when their order isn't fulfilled, about not been able to get the thing they didn't want 6 hours ago.
tapping into that, to prime the pot for downloads is surely a useful feature. The fact these apps exist are just natural competition in the app store, against the app store.
It is that last bit that makes me doubt the validity of it as a business model.