Mobile developers may wish to sit down and hold their jaw in place for this shock revelation: it's not easy making money from paid Android apps.

It's a widely-held perception within the developer community - and that includes a lot of people who are excited about Android as a platform - that Google's Android Market store has been something of a graveyard for paid apps.

Some blame the billing system, others blame the lack of discovery features, and some even suggest that Google has a deliberate strategy of marginalising paid apps in order to force developers to make their apps free and advertising-funded. You can guess who provides the ads in this theory.

The truth is likely less fun for conspiracy theorists: Google has simply spent more time iterating the Android platform in the last two years than it has on improving the aspects of its store that would give a significant boost to paid app sales.

New research from analytics firm Distimo puts some numbers to this. The company claims that while 96 apps have been downloaded more than five million times on Android Market, only two paid apps have passed the 500,000 downloads milestone - with six iPhone apps generating that many downloads in the US alone in two months this year.

Distimo also estimates that 80% of all paid Android apps have been downloaded less than 100 times each ever. It's worth noting that Google's laudable decision to publish download ranges for every app on its store is one of the key reasons why this kind of research is possible.

Anyway, the temptation to use Distimo's stats as a reason for developers and publishers who want to charge for their content to steer clear of Android should be resisted. There are a number of factors that should improve the prospects for paid apps in the months ahead.

Factor one: Google. In May this year, the company introduced a swathe of new features to the web version of Android Market, with plans to bring them to the on-handset version soon. They included new country-specific charts, Editor's Choice picks, a special icon for so-called Top Developers to help them stand out on the store, improved suggestions for related apps when someone is browsing the store, and a section to show currently trending apps. They're all welcome improvements.

Factor two: Non-Google Android stores. Amazon's Appstore for Android made a big splash when it launched in March with an exclusive on the Android version of the Angry Birds Rio game. Admittedly, that game was free, but one of Amazon's core features is that when it drops a developer's game or app to free, they still get paid a proportion of its list price.

Elsewhere, Amazon is promising to bring its famed recommendations engine to bear on Android apps, backed up by its position as one of the few companies whose credit card databases can be talked about in the same breath as Apple's. Meanwhile, mobile operators continue to talk up their prospects of launching curated versions of Android Market for their customers, with their trump card of carrier billing.

The point is that Android by the end of 2011 will have the potential to be a much more lucrative platform for paid apps, alongside its undoubted strength for free apps, whether supported by advertising or not. Developers are understandably wary of a platform that has until now combined greater porting costs than iOS with lower payouts on content that's charged for.

There is work to do on the fragmentation side of that equation, but the efforts of Google and others hint at genuine potential for paid apps in the months to come, and the promise of a return on brave investment made now.