There's several private companies that make money selling compilers: Green Hills and PGI comes to mind immediately. Open compilers are good enough that commercial ones have to be better in general or on specific platforms to justify price. Plus, they usually integrate into other tools that do things FOSS cant or doesnt do well.

One area that's an untapped market is compilers that automatically and efficiently protect legacy code. I've seen academic and FOSS methods that do well. A thoroughly tested, supported, integrated with IDE option would probably sell well. A cross-platform even better.