In anticipation of crossing the 10 billion app mark this week, Apple unveiled a list of its all-time greatest hits yesterday. Facebook, unsurprisingly, is the top free iPhone app in the world.

But what’s notable is how far the company’s platform still has to go in permeating the top mobile apps the way it has with half of the top websites in the world and in fueling the growth of multi-billion dollar social gaming companies like Zynga.

We dug through AppData to find out how many monthly active Facebook users the all-time top apps have — and it’s not that much, at least compared to the 15 million or more MAUs it takes to break into the top Facebook applications. In fact, the companies that break 10 million MAUs tend to get them from a cross-platform blend of web and mobile usage. (To be very clear, the data below is only representative of active users who elect to connect to Facebook. It is not representative of overall usage. If developers have more to add, they should feel free to reach out to us.)

The platform’s reach in mobile apps is important because one big part of Facebook’s multi-prong mobile strategy is to become more than a standalone app. Even though it has more than 200 million monthly active users on mobile devices, the company’s goal is to become ubiquitous social plumbing for web and mobile experiences alike.

With the introduction last fall of single sign-on, a dead simple way for Facebook users to sign up for mobile apps, the company is an intriguing dark horse player in the mobile developer space.

While Apple’s iOS platform and now even Google Android are starting to make it possible for there to be 50-million download megahits like Angry Birds, there isn’t yet a solid solution for the middle to long-tail of apps — a role that Facebook seems well-positioned to play. Although cost-per-install networks like Flurry and Tapjoy help, Facebook could also support social discovery of mobile apps the way it has on its home site.

Then again, one other (less likely) explanation for the low number of MAUs among top iOS apps is that while they’re seeing tens of millions of downloads, perhaps they aren’t engaging enough to retain an eight-digit number of monthly actives over the long haul.

All-Time Top Paid iPhone Apps

* – This number comes from a combination of web, canvas and/or mobile usage.
** – Pandora had an instant personalization experience early last year, but turned many of these social features off, resulting in a low monthly active user count.

1. Doodle Jump: 334,866 monthly active Facebook users
2. Tap Tap Revenge 3: None
3. Pocket God: 134,539 monthly active users*
4. Angry Birds: None
5. Tap Tap Revenge 2: None
6. Bejeweled 2 + Blitz: 11,353,705 monthly active users*
7. Traffic Rush: None
8. Tap Tap Revenge Classic: None
9. AppBox Pro-Alarm Clock: None
10. Flight Control: 1,800 monthly active users

All-Time Top Free iPhone Apps

1. Facebook: 62,187,311 monthly active users
2. Pandora Radio: 10,566 monthly active users**
3. Google Mobile App: None
4. Shazam: 130,476 monthly active users
5. Movies by Flixster: 789,918 monthly active users*
6. The Weather Channel: 60,199 monthly active users
7. Google Earth: None
8. Bump: 268,712 monthly active users
9. Skype: 3,224,868 monthly active users*
10. Paper Toss: None

All-Time Top Paid iPad Apps

1. Soundhound: None
2. StickWars: None
3. FlightTrack: None
4. Backbreaker Football: 7,528 monthly active users
5. Calorie Tracker: None
6. BlocksClassic: None
7. iFart Mobile: None
8. GoodReader for iPad: None
9. Cro-Mag Rally: None (relies on GameCenter)
10. Ambiance: None

All-Time Top Free iPad Apps

1. Pandora Radio: 10,566 monthly active users**
2. Google Mobile App: None
3. Movies by Flixster: 798,918 monthly active users*
4. Google Earth: None
5. Yelp: 9,104,755 monthly active users*
6. Fandango Movies: 40,512 monthly active users*
7. Remote: None
8. iBooks: None
9. Bible: 53,639 monthly active users*
10. Solitaire: None