Virtually all of my students want to sing pop/rock/etc. music when they first come in. My usual approach is to agree to work primarily in the genre of their choice, but to have some "classical" training as well. I largely due this in order to promote healthy singing, whatever the genre, so that no matter what kind of music they want to sing, they are at least not harming their voices.
Notice that almost all of Friedlander's comments focus on the relaxation of the vocal mechanism ("Like the first singer, he performs with perfect legato, clear diction, and a consistent, organic vibrancy. He arranges his resonance space to create a shallow snarl without setting up any resistance for his breath", etc). I've found that, above all, some classical training seems to reinforce this, allowing students to create resonance rather than merely screaming, to avoid straining at the edge of their ranges, and to approach all genres with a strong grasp of basic music skills. Of course, all of this also improves their basic technique immensely-- pitch, diction, and aural skills are usually highly improved as well.