You make is sound like Open Source projects just open up a source and let anyone throw anything they want into it. However, the code is usually checked quite well by project managers before it is included. Second, most often, programmers are put onto projects in the commercial sector. They code because they are paid. In the open source community, the programmers are there because they love what they do.
More care is put into that code than any other.
That is why is it faster and more stable. You make it sound like open source apps are stable simply because they are minimalized and simple. This is not true at all. Open Source software offers the same functionality you would find in other systems, and sometime more. It is the care that is taken because of the love of the art of coding.