Up until recently I worked at a large mobile publisher and we spent out-of-this-world sums of money to advertise games once the LTV was modeled and we had a high confidence level they would be profitable.

Ironically, App Store distribution is becoming nearly as difficult and cost prohibitive as pre-internet game retailing. Everyone is competing for the same limited shelf space and end caps. Once a network of games is built cross promotion is helpful, but entering the market is extremely expensive. You either need to win the featuring lottery, have something that is organically viral, or know your LTV and spend tons on marketing.

Unfortunately it seems the most surefire way to build a top 100 mobile game nowadays is to partner with a big publisher in order to leverage their marketing dollars and cross promo network. Hopefully some of the early indie link sharing cross promo networks will do some good to change that.