When explaining the early exits of the powerhouses, I'll stick with my "hackneyed excuses" (remind me how injuries, home-field advantage, and quality of opponent became excuses?). Your premise--that the World Cup is a lower-pay activity for the pampered, and thus leads to underperformance--is simply wrong. The Cup is the great player's ticket to immortality and all its attendant financial and female benefits. Conversely, a poor World Cup for a great player can destroy his reputation. David Beckham was demonized in England after 1998; Juan Sebastian Veron said Argentina's exit will haunt him for the rest of his life; Batigol and Crespo were bawling after they were eliminated; I am sure there will be tomato-wielding maniacs to greet the Italian team.
Indeed, there's no evidence--from this World Cup, or from those past--that teams with pampered players tend to underperform simply because they are made up of pampered players. All of the legends of the World Cup--from Pele to Beckenbauer to Zidane--were pampered players. Only seven nations have ever won the World Cup, every one of them laden with well-paid superstars. Having watched every minute of every match of the current WC, I don't think the French, Argetinians or Italians were ever seriously out-worked (save for Italy v Korea). All three were extremely unlucky to lose their matches.
As for your list of "hard-working teams", outside of the astonishingly fit Koreans, it's a curious one. The success of the US and Senegal has been mostly due to the counter-attack and luck (both teams were literally inches away from being eliminated). Turkey have certainly fouled a lot, but I wouldn't say they've lit the world afire with effort. Japan only impressed once their geriatric opponents, Belgium and Russia, had wilted; they were horrid against the Turks. Ireland and Denmark have been very hard-working, but then again, they're filled with stars from the world's richest and most prestigious leagues. One might even call them "pampered".
Finally, regarding the relative success of Groups C, D and F: if you want to draw conclusions based on six matches, go right ahead.
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