I'm not living in the USA, but it all depends who's taking care of the financing. Here were I live we almost have no support from government or private publishers or production firms. That's when I decided to try to make a living on my own ideas. But in most cases it seems that really have to find the money to live on my own. I'm taking risks and I'm sure these higher paid guys also are taking lots of them.
And the most important is that you're awake when a deal gets setted.
It's like the singer from my band who declares "hey man, i've got 50 songs ready to record", then I say , Ok , but will you do all production and finance 4more albums at your risk??? That's the point where they mostly stop talking and wining. Everybody out there has some minor chances to make it out there, luck is an important factor, but eventually everybody could reach everything as long as you live for it and try to work as hard as you can. And mostly people start complaining after something has become a major succes, instead of gathering some money themselves or find partners to produce stuff with.
And like some off you said, bills don't always explain what's kept left from these kind of productions after taxes and expenses.