OS Application Stores v/s Mobile Application Stores

Recently i came across this Airtel App Central, isn't it strange?? I mean at first I too took it normally but after a while what came into my mind is why a service provider is opening its application store as we already have application stores from the OS providers (e.g. Android Market, iPhoneApps, OVI store, BlackBerry App World etc), what are the benefits of having an application store?? will the users go for their application when they already have inbuilt apps from OS manufacturers?? also they are charging more than any other OS-App e.g. Airtel is charging Rs 1 per day for some of its applications.

Initially it was quite weird for me but the statistics ( link ) surprised me even more and made the whole mess a lot clear. So here is my observation about the whole story. Why they are successful.

• Mobiles with low cost: Mobile phones below Rs. 5000 almost do not support any OS application store, this is one area where service providers can have advantage. Since most of the phones today are GPRS enabled and supports java applications, this user group can be a big market for service provider's apps store. This is very clear from the stats of Airtel apps Central.
• User's are not stuck with a handset: Second advantage is from the users point of view, a lot of time it happens that they change there handsets and finds it difficult to download the same applications for their phone. Also service providers keeps a track of your purchased apps and downloaded apps which you can use on any handset with your simcard in it. Let us say I changed my phone from Nokia 5800  to Xperia X 10 mini. Now I have to download all my favorite apps again and will have to pay for it again. Suppose I've used all the Airtel apps before, means they can be downloaded on the new phone as well thus saving a lot of time and money. 
• Buying Process: Buying an application from OS App store is quit long and requires credit card/paypal account etc, while with mob app stores the amount will be deducted from balance. Today in India very few people have credit cards/paypal accounts which means they will prefer the mob app store.