I guess it's a question of what the company is selling. Google for example uses huge stacks of open source to run their business. And even though they are far from being pure open source, they do contribute back to the community in multiple ways, for example with contributions to the Linux kernel and open source projects like Chromium and Go. And then there are projects like Qt, that mix open source tools with enterprise support.

But I think that the field of IT is still extremely young and that in the future larger companies will discover that collaborating on open source platform and infrastructure projects will give them much better synergy effects and lower IT costs by removing the license cost and at the same time lowering the support cost. Compared to history, the 20-30 years that mainstream computing has is really just a spark and there is so much change coming that will be directed by market and competition.