When installing an app via the Market app on a phone, the app will correctly receive the referrer information passed to it (as described here: http://code.google.com/mobile/analytics/docs/android/#android-market-tracking).
However, when installing the same app with the same referrer via the web-based Market, the referrer information is dropped and isn't received by the app. This makes campaigns targeting your app from the web impossible to track.
Is it possible to track install referrer via android web market?
No, it is not possible to track install referrer from the web-based Google Play store. This is a known issue with the latest SDK.
Google Play Campaign Tracking does not currently support web-to-device installs initiated from the web Play Store.