why does the 10C cost more then the 14 what does the 10 have that the 14 doesn't

That is a dang good question . I have both the 10cg and the 14sg and I prefer the 14 it has far better programming options. So why the huge price difference for fewer channels. I will admit
I dont use all the bells and whistles on either tx so maybe I am missing something

Futaba hasn't said. That's just how the pricing works out.

I have a14sg TX and in the manual I read that in the fasstest 12 that you can't run analog servos is this true

That is correct. When operating in 12-channel FASSTest mode, you cannot use analog servos. That's because the servos are being updated faster than usual, which causes problems with analog servos. You must use digital servos when in 12-channel FASSTest mode.