As mentioned before, It isn't by acccident that only 7 nations have ever won the cup. I do not doubt the major teams motivation by bringing their best player and by fielding them. What I am saying is that a WC preparation for the major teams has nothing to do with a confederations cup one. You can see that once we enter a WC year everything is done for the players to be at their peak both mentally and physically when the WC starts. As soon as the qualifiers are over and the draw for each group known, tactics and players are in place. Of course there are injuries or final adjustments but if you plan on winning the WC you come ready and prepared.
The top leagues always has a different flavour during WC years. Starting 2010 few months before the WC kick off, all the talk will be about the WC. The audience, commentators and the players feel it. Most players live for the WC and winning it is their Holy Grail.
You are absolutely correct in pointing out that the US needs a high quality soccer league but they also need serious opposition in the international level. Other nations have the Euro, Copa America, Asian Cup and African Cup all them which are of a higher level than the CONCACAF golden cup and some requires serious qualifying matches to even enter the respective competitions. Apart from Mexico the US team are never challenged in the WC qualifiers nor the golden cup. Friendlies are to be taken literally, a yellow card is a rare sight, no intensity what so ever and everyone gets to play by bringing in 5-7 substitutes.