This is usually because the app would not work on the Vox, ie: needs GPS, Bluetooth, phone network etc or some other features the Vox doesn't have.
If you were re-directed to the Google Play Store, you would also be unable to get any apps because the Vox does not yet connect to it.. Hopefully soon...
In the meantime you can get apps from alternate stores like the Goodereader app store, slideme, Aptoide which don't connect to the Google market.
http://m.aptoide.com/
http://goodereader.com/apps/category/android-apps/
http://slideme.org/application/slideme-marketplace