Focus on the users who do say the "Thank Yous", post comments and clicks "Install" rather than on the users who don't.
As for the installs, what constitutes as a "fair count"? You'll never know the true count and frankly it might be far off from the downloads count. Especially if the download count tallies up all downloads instead of unique user downloads. Then again, maybe the users who've clicked "Install" did so just for kicks. Too many uncertainties.