I feel like the decision to have women sing the songs (not to mention the fact that they sounded so great) says alot about Kurt Cobain and his music.
First off, I applaud this decision because it seems to acknowledge the sad dearth of male singers who pitifully try to emulate Kurt, or simply have nothing to add to his songs with less interesting vocal performances. Really, the only way to do a nirvana tribute without it seeming like corny Karaoke is to have women sing.
The fact that it worked so well is a testament to how truly androgynous Kurt's work and legacy is. Kurt was never David Lee Roth, Paul Stanley, or even Henry Rollins.. his lyrics and message were never about being a man or limited to a masculine experience/perspective.
Again, incredibly happy that they executed it this way.