.app extension in Spotlight or Alfred
I believe that unless you have "Show all filename extensions" checked in Finder's Preferences, the .app extension is hidden by default. If you were to look at Sparrow in Finder, do you see the .app? If so, open the Get Info window for it (Cmd+i while highlighted) and make sure "Hide extension" is checked. You would have to check each app that is showing its extension manually.

Another thing is that if you have more than one of the app, I think it will always show the extension in Spotlight.

If none of that works, you can always try rebuilding your Spotlight index: $ sudo mdutil -E /