But that doesn't mean that is the most widely used. Its nearly 3 times the cost of a 5D that is more than capable of taking professional grade photos ( besides speed, if you need to shoot low light sports ) so there is a point where better becomes irrelivant. The point I am trying to make ( regardless of brand ) is that cameras become popular due to how much they are used and touted by professionals. Plain and simple, thats how the consumer guages a cameras worth. So to answer the OPs question, I think the caveat missing is the price vs quality vs practical needs of a professional argument. There is always going to be something faster or higher res, or whatever, but what do YOUUUUU need to do the job the cheapest and most efficient way possible. I think THAT answers the question as to why people tout those cameras as being great cameras. I think they are the cheapest price point that really encompasses most of what a professional needs.
You do make a very good point that value is something to factor into the decision to buy a camera.
You are also correct that the D3x is not the best camera for action/sports shooting. Something tells me that if you can afford a D3x though, you can also afford to buy another one to be your go-to sports body.
I tend to throw things like value out the window when determining best. I realize that not everyone looks at it this way.
By best I meant overall. Out of the possible things you can do with a camera, action/sports shooting would be 20-30% of the total at the very most.
I also realize that to some pros action/sports shooting is really all they care about.
One things for sure. Nikon and Canon both make some damn fine cameras...