No that's one-dimensional way of thinking. Consider this: by developing OSS, they expand their share, which in turns someone else gets shrinked (M$). In long term that brings more money. Another example: Google and Android. They have found a way to steal a huge number of Java developers by cleverly designing Dalvik, and allowing developers to use their favorite tools. At the same time closed-source competitors are shrinking, no matter how good their products are. I think you may find a fair number of OSS project which became dominant over their closed-source counterparts. Apache web server is an excellent example, or MySQL before the Oracle got it.