CMU here also. I graduated several years ago, but I distinctly remember groups of CS students banding together to create things on their own. That's start-up culture. You get a bunch of motivated, technically inclined people together and build something. The CS undergrad lounge always had people fiddling around with things and geeking out.
At CMU you are free to do what you want with your spare time. There doesn't necessarily need to be a class for teaching start-ups. A class can simulate anything (DDOS attacks, power outages), but whether or not that simulation is a reflection of reality once the student leaves the classroom remains to be seen. Furthermore, if you need a class to learn something, then there are many hard lessons waiting for you in life.
The reason you get a CS degree at CMU is to become a better problem solver. It's a very difficult course of study. When I was there about 1 in 4 students dropped out of the SCS program. If you make it through the program, it is a badge of dedication, and you are definitely transformed into a problem solver. The environment in which you use these problem solving skills - at a start-up or a large corporation - should never be an issue, nor should it require explicit handling.
Often when I see a start-up populated with dropouts I'll think "They couldn't even make a 4-year commitment? Does that mean they'll only stick around here for 2 years before they split?" And that is often the case. The infatuation with dropping out and start-up "culture" is purely romantic.