I don't think that this is actually true - most of these songs are purchased from agencies, produced to within an inch of their lives, and marketed aggressively in every possible medium. People may like the songs (and they should, because every part of the process has been managed by the most talented and successful people in the music industry), but that's not specifically the reason for Miley Cyrus's success.
Biley Papyrus could have the same songs in the same order on the same records with a sound produced to be indistinguishable to the versions you're familiar with, and if Biley didn't have the brand that has been created around Miley (or Rhianna, or any major corporate pop artist), Biley's success with that same set likely wouldn't be what Miley's success has been.
edit: Also - Smiley Papyrus (Biley's sister) could have the exact brand as Miley, and an entirely different set of songs, and the expectation would be that she would be successful. Hell, when Miley puts out her next album, she pretty much is Smiley.
* Have at least some baseline modicum of talent * Have access to talented songwriters * Have access to talented producers * Be attractive, or at least interesting to look at * Have a stage presence
Bonus points for: * Ability to dance * A salacious or intriguing "private" life
Many pop stars have singing talent in spades (Beyonce, Adele, Whitney Houston), but many others have proven that extraordinary singing talent is not a pre-requisite for enormous success (Britney Spears, Jennifer Lopez, Miley Cyrus, perhaps Madonna).
I would say talent is less important now than ever. But this could be an illusion, as history is likely to forget pop stars who leave behind nothing memorable.
Britney Spears and Lindsay Lohan are not exactly long-term success stories, even though they continue to be in the news and their popularity is still worth money.
These documentary clips about the "pop star formula" (boobs + hair + autotune + writing talent from elsewhere) are rather instructive:
https://www.youtube.com/watch?v=soNLWoSMy1k
https://www.youtube.com/watch?v=Z9tpOvYDqyo
(the 2nd clip about 1:30 applies the formula, humorously)
Put it another way: it doesn't matter if your song is good for many people, if you can't reach them, nobody will know about you.
If so, I don't think it's a correct assessment. Her music is ultimately popular because people like it. I don't think people think Wrecking Ball is a better song because the video was over-the-top, nor would a wild video make me like a song I would otherwise hate. Miley was also popular before she got more extreme. On the flip-side, Britney Spears was far more popular before she got extreme. I'm sure there are other cases where an artist receives more press attention that does not correlate to increased music sales.
Chris Brown has had nothing but bad press since he hit Rhianna a few years ago and he's still placing songs on the charts and radio. People seem to mostly dislike him, but will still listen to his music. I don't think they're listening to him because he hit a woman and is in and out of jail. I think they just like the songs he makes.
In the end, people still need to have some connection to the music. In pop music, that connection may not be entirely rational, and it certainly isn't lasting, but it's still there for some period of time.