Some of those open source software packages are as good or better than commercial products. The better ones have huge followings and plenty of support, as well as large user bases full of people more than happy to offer a helping hand when someone gets stuck.
Remember -- open source does not mean you are necessarily talking about a stripped down, awful piece of software. It simply means the code is free to all who want to see it and modify it. Often, your larger open source companies make their money through support, custom software design and through other ways.
For example, let's say you have an open source Web development platform. Plugins -- small applications that improve the functionality of a platform and sites running off of it -- are very popular with those. The company that built and maintains the platform might charge companies that want to market plugins for the software.