If you want to create a direct link without redirection of App-Store: follow this:
Copy iTunes link, for example: http://itunes.apple.com/linkmaker/
now, replace the http:// with itms-apps://
now you can open the link using UIApplication, for ex:
[[UIApplication sharedApplication] openURL:url];
and the one important thing is that the link will work only on actual device, it will not work on simulator.
Be careful, those links only works on actual devices, not in simulator.