Spiderweb throwing in the towel I would guess has a lot more to do with their #1 point "Competition on the App Store has risen to a frenzied level." than the others.
The top two grossing games - Clash of Clans and Game of War - receive metacritic scores of 74 and 67 respectively.
Whereas the most recent SpiderWeb release I can find - Avernum 2: Crystal Souls - sits at 81
The organic discovery issue is only a small component of the problem when you look at the sheer amount of money that the micro guys can afford to dump into the mobile-advertising economy.
And as anybody who's spent 5 mins on app-store "optimization" knows - the better your paid, the better your organic - by a right mile.
I hate ending comments like this without a solution but the best context we have is watching Zynga get eroded / replaced on FB at some point.
But their death blow was the rise of FB's platform selling ads to the mobile OS guys mentioned above who essentially just out-zynga'd Zynga.
When you create an app economy that provides outsized rewards to the vultures, of course they'll control the board, wonder where this winds up.
(1) http://www.metacritic.com/game/ios/clash-of-clans, http://www.metacritic.com/game/ios/game-of-war---fire-age, http://www.metacritic.com/game/pc/avernum-2-crystal-souls