One important thing to remember is coping with a first build on a new machine. Having a squeak app that can drive cc to build a vm would be very neat, but if you don't yet have a working vm for a device you could be in trouble.
An advantage of the cmake process is that it bypasses that issue. Actually running the configure on the target machine means you get (hopefully!) accurate results when querying facilities. There is also some benefit in a production environment in being able to pass a 'normal' build job to someone else without having to find a squeak buildomatic cognizant person.