Curious - how come AppDiem didn't take off? Something like that around early 2011 really could've taken off and helped with the app discovery problem. I know now there's a ton of players in the space but still!
Most of the developers we were scheduled to release ended up bailing to go to Amazon. I was the developer, and by launch day most of the heavy lifting was done (only took a couple weeks to build as I recall), but my partner was the marketing guy, and had all the relationships.
Right after we heard about Amazon's thing, he had some personal crises arise and ended up bailing. I don't fault him for it, as he had some decidedly real real-life family drama, but I wasn't even remotely equipped to handle the failure as I didn't know who had bailed or how to fix it.
No doubt that discovery is something that really could've changed the app space dynamics. Something similar happened at the place I used to work - a lot of top devs were reached out to by Amazon and they initially disallowed in app advertising. The developers complied and it caused a slight panic.