[jsphweid]

As other posts point out, leaving out the third takes away the major-ness.

It's also worth mentioning the way Kurt often played power chords, using his index for the bass note and barring the rest with his ring finger. This often leads to major chords when the root is on the A string and non-major ambiguous-sounding chords with the root is on the E string. It's obvious as early as the 3rd chord in the intro to Teen Spirit; it has the notes Ab Eb Ab Db (NOTE: Db, not C). It's inconsistent in Kurt's playing (edit: whether or not his strumming makes that 4th string, 4th interval sound come out), but the subtlety is a signature part of Kurt's guitar sound.

Also some of the chord analysis in the site (ex. In Bloom verse) is just flat out wrong.