No, the US isn't running out of good fighters, they just aren't being exposed.
If you look at alot of Side companies like WEC, RSF, IFA and others they have some good fighters that are on they're way up. Its also hard to judge american fighters from TUF show lol, alot of the fighters go to PRIDE, K1, or even just WEC.
Trust me there are tons of world class fighters in the US, you just have to go outside of Spike TV at 10 at night to see them lol.
I also have a good theory behind TUF 4, i think Dana did it because right now he has to many TUF fighters that he's trying to work into fight cards, and with the TUF people who already fought on cards all they have to do is win, and then they get the title shot, no worrying about hypeing this guys up and makeing sure they can fight other UFC fighters.
What is it that is going to be on your mind when you're on your death bed? Will it be the tedious years of 9 to 5, or the memory of some great acheivement. Maybe a moment you stood in glory to the applause of millions.