Not all internet startups are web startups. In my case, I'm working on online backup, and every single line of code I've written for it has been in C.
I'm not going to suggest that you should get into the same field and start competing with me, but there are many options under the umbrella of "infrastructure services" which all require highly efficient coding.
Certainly. Although most internet startups will include a strong web presence, that is often a small part of the equation. I got pretty heavily flamed for suggesting to not write your own framework, but I think the whole point was different business genres.
For an internet startup, you probably don't want to write your own framework. For a web based startup, where that is the core of your product, you might have a huge competitive advantage writing your own.
I'm not going to suggest that you should get into the same field and start competing with me, but there are many options under the umbrella of "infrastructure services" which all require highly efficient coding.