If all music were the same in “character” there would be no need for titles or descriptors. If opera singers could do rock music and rock stars could sing gospel tunes and folk singers could walk onto a Broadway stage and sing a traditional show, we wouldn’t need categories. The Grammy awards wouldn’t have categories, either, nor would Lincoln Center Library, which has even more of them than I was aware of prior to going there. The attitude that everything is the same seems to imply that all music is a spin-off of classical music, and all good vocalists can sing classical music easily and therefore, they can also sing well in any other style, as  all other deviations are simply “individual” interpretations of songs.
So, if you are Paulo Szot, and you sing “South Pacific” and then you go do an opera at the Met, are you a “crossover” artist? [Yes and also no.] If you are Michael Bolton and you record opera arias on an album, are you, too, a “crossover” artist? Does Mr. Bolton sound like Mr. Szot? Not in terms of his own voice but in terms of how he produces sound? Does Renee Fleming sound like a rock singer on her album of “rock songs”? The NY Times reviewed her album “Dark Horse” and said, “Ms. Flemingâs next step is figuring out how to sound, now and then, just a little less serious about it all”.
So, as long as there are different kinds of sounds in different kinds of music, we need names to define them. Within each category, there are all sorts of variations, all sorts of artists and there are no “border police” between one style and another, but until and unless we acknowledge that there are audible differences, we are left to confusion. The public decides and the public has its preferences. We are left with facing the reality of today’s music business, messy as it may be. You can’t train anyone from such a vague place as “everything is the same” and you can’t direct someone toward reasonable vocal and musical goals if all you know is the “it’s all one thing called singing”.
The origin of the terms of each style is interesting to contemplate. Maybe, some day, there will be a new style that emerges and hits mainstream. The last one to do that was rap, and that’s more than 20 years ago. It will need a new designation, too. Until that time, we have what we have.
If you are a rock/pop/gospel/folk/jazz/country/broadway/classical vocalist, good for you. Just don’t confuse the Nashvill rep with An Die Musik.