While Microsoft’s Windows Phone 7 (WP7) Marketplace tries to assert itself in the competitive world of mobile app stores – in the US download volume is 39 times smaller than Apple’s App Store for iPhone – some interesting regional trends have emerged from research by app analysis firm Distimo.

Around half of all apps on WP7 Marketplace are available in the 17 countries in which it initially launched, with around one-third present in all 35 countries it now reaches. Some developers have clearly failed to take advantage of the Windows Phone 7.5 update which added the new countries to the ecosystem, showing there is an opportunity to increase downloads.

Just under 6 percent of applications in WP7 Marketplace are available only in a single country. The US and Japan have the greatest number of unique apps with 1,361 and 215, respectively. A number of countries – Chile, Colombia, Portugal and South Africa – have no unique content.

There is a degree of overlap in terms of the most popular apps across countries though. In general, paid apps have a greater overlap than free apps, suggesting free apps are more localised. The graph below shows that the countries that were part of the original WP7 Marketplace launch have more apps in common. For example, Australia and the US have 67 percent of the top 100 free apps in common.

However, it seems Japanese developers in particular find it hard to translate local success with free apps into success abroad, with just 21 percent of the top 100 free apps in Japan making the top 100 in the US. Distimo says this is because Japan has a high daily download volume for free apps but a low level of apps that translate to other countries.

Games make up the most popular app category in WP7 Marketplace globally, with a third of the top 100 free apps being games and 54 percent of paid apps. Tools and Productivity, Entertainment and Travel and Navigation are also popular categories.

However, the proportion of free apps that are games varies considerably between countries, with the top 100 in the US and Australia having 50 percent games while Brazil, South Korea, Norway and The Netherlands have between 15 and 20 percent. The range is even greater with paid apps, with 64 percent of the top 100 paid apps in South Africa being games but just 10 percent in Brazil and South Korea. This difference is related to the ease developers have in submitting games to the app store in these countries due to local game rating policy, according to Distimo.