Beyonce has 'it' - whatever it is. Like others before her - Michael Jackson, Madonna, etc - some performers have a type of larger than life charisma that shines and Beyonce has that. You can see it in her performances, in her movies, etc. Even though she's a worse actor than Madonna...when she's on screen she radiates.
Ah'll show you crazy!
Having 'it' is not dependent on talent and all the marketing/critical praise/etc in the world will not provide a performer with 'it'.
I have my theory about the 'instantly memorable/recognizable voice.' I think Beyonce has one of those. Not suggesting she's a good singer or anything of the sort, but once you've heard her voice, you will always know it's her. Just as you'll always recognize Elvis, Janis, Rod Stewart, Whitney, Michael, even Madonna's little chirp slash menopausal growl...there's a quality to the voice that makes your ears perk and pay attention, even if you don't want to or find it ultimately displeasing.
Kelly Rowland is probably a superior voice and singer to Beyonce...but there's nothing memorable about her voice, her tones, her delivery. But you hear Beyonce screech through Single Ladies and months later you'll watch a room full of drunk irish Catholics at a wedding reception not only sing along knowing all the words but the dance moves as well!