I'm not sure I agree that the frame's less important on a fixed. I think the most important part of any bike is the frame.
I'd also say that there is such a thing as a bike that's too light. Fixed-wheels tend to be light anyway. Make then super-light and they'll be skittish, made all the worse by the lack of freewheeling capability.
I'd also say that there is such a thing as a bike that's too light. Fixed-wheels tend to be light anyway. Make then super-light and they'll be skittish, made all the worse by the lack of freewheeling capability.