Let's clarify that headline a bit. It's perfectly fine for Kelly Rowland to do a Whitney Houston tribute; she, and almost everyone in R&B these days, owes her career in part to Houston's influence. And although this really isn't the time to play the "but is she Whitney! Nobody can be Whitney. But how Whitney is she?" Olympics, Rowland's a better vocalist than a lot of people give her credit for.
That said, there's a fact that needs to be acknowledged. Paying tribute to a singer who's influenced you? Fantastic. Having Stevie Wonder do it with you? That just ups the game. Just a bit. And doing so at Muhammad Ali's birthday celebration? Even more. (The track Rowland chose, "The Greatest Love of All," was originally recorded for an Ali biopic.) There will undoubtedly be plenty more tributes in the days to come; few, outside Houston's official remembrance, will be this well-sung and have such prime guests.