Let's not confuse a good voice with a good ARTIST. One may have Louis Armstrong voice and make miracles with it and with the songs, and may have Domingo's voice and be unable to sing a tango acceptably.
BUT, the most important, in my opinion, is to never assume that a good voice is not necessary for a singer, or not necessary for certain repertoire. For example, listen to Kiri Te Kanawa - she is an "operatic" voice indeed, and possibly her high pitch will sound hard to the ears of Jon and many people who dislike this form of singing, but HOW SWEET she is when she comes to intimate songs, even to popular and maori native songs, and so many different kinds of music!
On the other side, listen to Shakira (one of top sellers in Latin America, hope you know her): she seems to have a good timbre, but insists, purposely, in a nasal sound full of unnecesary "breaks" which will ruin her voice in a couple of years. Of course she sings things A LOT EASIER than classics or even jazz.
One word about the "operatic" sound: this is the sound of human voice, magnified only by vocal technique, in order to fill a theatre (you should never sing in open air) as it was known until amplification arrived. One should understand this before comparing the sound with any popular singer of the XX century, who were born with a Mic on their hands. Did you hear old Italian songs, English madrigals, Spanish romanzas ? They were the popular music by those times AND THE VOICES WERE TRULY "operatic" TOO ! Because there were no mics.
As the electric amplification comes to our lives, we start to hear NOT the human voice, but an imitation made by an electric circuit and a paper cone activated by a piece of carbon. Even we hear the same when we attend our artist's presentations. Then EVERYBODY , even who did neither have the VOICE nor the TECHNIQUE, could raise his voice and it was necessary only the art and the sensibility, to reach the audience ears and hearts. I find this is NOT BAD at all, but it is not THE voice, not THE singing.
Hope I had contributed to a deeper confussion :))
Un abrazo - Andrés