They kind of say: "look good, sound good."
Having worked in this industry myself, is it definitely a talent to have good stage presence, good presence in front of a videocamera, photogenic and modeling skills. Not to mention charisma when dealing with radio and TV interviews, fanbase, etc.
It's also a talent to sing well, to sing consistently, to be able to channel inflection and emotion on command in a studio or on a stage.
There is more to being a pop star than the songwriting.
(Note I'm saying all this while still holding huge respect and value for the songwriters and producers themselves. I'm a total music fan.)