The question is do you think The Beatles, Elvis Presley and Johnny Cash were talented enough that, had a service like iTunes or MySpace existed at the time, they would have had their big break regardless, simply because of their immense talent?
No, I don't think so. they all are great for several reasons, one of the most important of them is that they had big companies investing money on them. Otherwise they could not have had spent a whole year recording one single album in studios like Abbey Road. No money = not this time to produce music = less quality albums. How many records currently can afford to pay an entire orchestra on the recordings for, lets say, a week? It's the Britney Spears, Paris Hiltons and Justin Timberlakes of the world who need to worry about not being discovered if producers and managers are taken out of the equation, not the David Grohls, Eric Claptons and Neil Youngs.
don't you see you have mixed current bad artists with good classics? (where are the contemporany classics?) currently companies only spend money on things they're sure they can sell and this is causing no more Neil Youngs and a continuation of several Britney Spears and co. In fact, if interesting labels are closing, who will promote a good artist? a non-proffit association?