Well before we go into this, let's clarify what 'Talent' really is.
The way I see it, and with context to this discussion, it's a two-fold definition :
One would be as you describe it, gaining the ability after hard work and effort.
And the other... Well.... you'll see as you read along.
It means that looks, whether they be natural or the result of hard work and cosmetic surgeries, should also be considered as talent. Secondly, performance and showmanship. Clearly the 9 girls of Girls Generation, or the 4 cuties of Secret are not the prettiest, cutest or sexiest girls in South Korea. I've seen countless that look prettier, cuter and sexier in my city's downtown. The same goes for Bieber. It's not like he's the hottest 15-18 year old kid on the planet or in U.S. In fact, I don't doubt that there are many that look better than him and sing better and have better vocal range. And of course, the same goes for those girls. The question remains, why them then and not someone else? And the answer is very simple, they have certain talent; appeal to the masses that induces sales, success and popularity. They know it and they know how to use it.
Here's a few examples of what I mean: (You will cringe watching this, but for educational purposes
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The top one is Girls Generation with the Aegyo (cutie face) battle, and the other is Secret with a Song called Love is Move.
Clearly Secret's vocal prowess is decent, but nothing really sensational... But, it's how they pull it off. Trust me, being that cute and sexy at the same time is not easy; but those girls make it look very easy don't they. And that is talent as-well.
That's exactly my point, you're not being objective. After all, Talent is defined as a NATURAL ability or aptitude. So on the terms of objectivity, having a vocal resonance, natural ability to appeal, either by sexiness or cuteness (for example) are talents. I understand what you're getting at here. Clearly, someone who was born with a great voice will still have to practice a hell of a lot to train that voice. I'm not sure if you and or anyone (well I'm sure you have) watched American idol, or any Idol for that matter. You see this during the audition weeks, countless potentials with really strong and powerful voices.. but, they sing out of key and completely miss the tone, and basically are all over the place. Some of them could be trained and become really great singers, and some simply don't have that talent of musical ear. So you end up with someone with a strong voice, but no control or any singing ability. Remember, having a good vocal range and being able to control is far from being naturally born with a strong voice. Trust me that this 'Taeyon' girl from the clip, although been argued to have one the best voices in the industry, has been training for years with SM entertainment. However, this is the key factor with true and natural talent or aptitude. Compare that girl with another member of that group, Yoona which is basically the visuals of the group. That Yoona girl has been with SM for the longest time pre-debut of the group itself, and was trained the most. Now, as for dancing, she's great, very sexy and cute, and she pulls it off. But as for singing? Well, she sings well, definitely not horrible or anything like that. But, compare her to that leader Taeyon, and no matter how much training she'll put in, she'll never reach that level. Simply put, not that talented in that aspect. But then again, pin her acting skills (which are impressive) against the rest of the group, and she destroys them no questions asked. I'm just giving you a little inside intel here for context purposes.
Remember that the 'looks' as talent is within the context of the Pop Music discussion. And yes, looking good is a talent.
Think of the definition, a natural ability or aptitude. If someone is naturally born with aptitude of looking pretty no matter what you throw on them... then it's a natural talent for being pretty.