Some advantages to have some Web Player :
- Share quickly any very early gameplay or level demo without needing to download or install something :
Just click on the link
....
You don't have to download 1Go each time to play

!
You actually download all data to your browser cache so this is not anymore quick, if it was a zip only additional step would be unzipping. You download same amount of data and still install nothing. If it's the first time webplayer has the additional downloading and installing webplayer step.
For people new to IT thing, that people probably wont be able to install a plugin if they can't even unzip yet, or be able to play your game.