I’ve been watching over the past few days as three separate studies were released, each with a different angle on the growth of mobile apps. These are generally orbiting the AppNation conference that took place this week in San Francisco.

First, ABI forecasts 44 billion app downloads by 2016. To put that into perspective, Apple recently passed 10 billion downloads and Android has seen about 3 billion. This is a lot of growth, but don’t rule out the mobile Web as we’ve argued.

Next, Distimo has released its latest report, this one zeroing in on the relative sizes of smartphone app marketplaces. Surprisingly, Android (134,342) has surpassed iOS (121,845) for free apps available. Apple still wins for overall app library though.

The higher proportion of paid apps for Apple has a lot to do with its superior payment platform, which makes it easier for users to pay, thus incentivizing developers. IOS has also had in-app payments for some time, while Android only recently integrated them.

Lastly, Nielsen is out with fresh data showing affinity for competing smartphone operating systems. A key part of the data shows that iPhone users are most app engaged when it comes to average number of downloads and usage frequency. Not a surprise.

The data also show that iOS and Android users make up 74 percent of the total market of app downloaders. Panning back, overall smarphone penetration continues to creep upward — now at 36 percent of U.S. mobile subscribers, according to Nielsen.