You'd probably be surprised at how ordinary most of the talent are. Obviously there are a few that believe their own press, but they're not usually the ones who'll be around for long. Being a star is a small part of the job, laying down vox is another. You know when somebody will be around in some capacity for time because they know that their performance is just raw product.
Ke$ha got her contract the same way as anybody else - somebody who could afford to pay the likes of me thought that she could be shoehorned into the white dancer/singer package, as created by Madonna and pillaged by Britney Spears, that would sell. Simple as. They were right. Does she spend her time off camera strutting about self consciously aggressively flirting with her bare flesh, but still managing to lead with her lip gloss? Does she bollocks! She's a dancer, she lopes about in sweats with her hair tied right back and battered comfy trainers on her feet, probably some kind of lip balm to make sure that dehydration during run throughs doesn't do anything to her lips that'll make her make-up artist tell her off...
It's the same with anyone. Think of whomever you consider to be someone whose recording contract was a foregone conclusion due to sheer talent and i could show you somebody equally talented whom you've never heard of despite them having been around for the same length of time and having had all the self belief and perseverance to keep plugging away in the hope that they'll get a deal... and who knows, they might...
The bloke who could have been Tom Jones if there wasn't one already, but writes his own material too, may get a gig singing his heart out at a piano... if demographic and economic projections suggest that middle aged women will see on average a rise in disposable income within the next financial year.
There's a superfluity of white 'family friendly' boy/girl bands reaching an age at which the spotless character is starting to wear a bit thin and they are branching out into slightly more risque material in the hope of developing a new market, say. Time to get some new sparkly young wholesome white virgins on the job? Don't panic, there's a never ending supply of them in the pipeline. No, time to call that kid whose voice became really distinctive as they grew older until they got quietly dropped even from backing vocals, b/c the bv's aren't supposed to upstage the talent, because you can bet your arse that the boy/girl bands cannot help but look a bit plastic as they "grow artistically" - time to unleash the "real", the voice of da street... the Rolling Stones to their Beatles.