Watch the Kurt's Grunge online guitar lesson by Angus Clark from Hard Rock Survival Guide: Rhythm
Pay close attention to the chord voicings here and the strumming in the right hand. Kurt Cobain's approach was much more from the acoustic strummer/Beatles school. In order to survive as a guitar player, you need to be able to change your approach depending on the sound desired by the artist you are working for. These should be choices that you can make in order to serve the good of the song. With all of the different techniques at your disposal, you're not limited, you get to choose. This is an example of that.