Maybe I shouldn't say irrelevant, but sometimes I think we all worry about this too much. If you have good singing technique and a healthy pleasing voice, are you really limited to one (or two) genres of singing? Granted one needs a feel for any kind of music and it's pretty hard to teach that one. But many musical sorts of folks are fully capable of "getting" many and maybe even all types and genres of music. Different voices are clearly suited to different types of music, I'm not going to argue that one. Case in point, I am not a big fan of Rod Stewart singing standards. He certainly has a great pop/rock voice, but crossing over into the Great American Songbook is just not anywhere I need him to go. (Not that he cares what I think, I'm sure his bank account has more to say about that then any music critic). Same with many classical singers taking on pop songs-"Gag" say I, for the most part. Two totally different sounds, both of which I lovingly embrace as a listener, that sometimes just don't mix well.
However all of that being said, I myself am a genre buster. Two weekends ago, of a Saturday night, I sang a gig with my roots band, and the next afternoon, (!) I sang at a benefit for Jaroslaw Golembiowski's Chopin Society at the Chopin Theater. We performed several of our original songs which, seem to breach a murky gap between art song, theater song and European cabaret. I've only recently been back to performing this sort of thing, and I'm not going to say it isn't a bit challenging to go from one to the other in a given weekend. (The main challenge being that I was exhausted from singing a long couple of sets the night before into the wee small hours...) But I feel good about my ability to get inside of a rockabilly tune or a Lucinda Willliams ballad one night, and switch to a highly cultivated art song based on very personal poetry the next day. Not to be braggin' on myself, just to be sayin' if I can do it, so can others!!!