There's also a lot of business value in freeriding when the software license explicitly allows you to do so.
Sure, the business values I mentioned are like 'extra income' over the free-riding 'income' you mention.
(Now this makes me wonder how to book the use of open source software in management accounting)
It's also free on-the-job training for your in-house developers, and it probably also helps your company when you're recruiting developers--you can look for potential employees among the other contributors to the same OSS project your company uses.
First of all, by contributing, you show a mutual interest in the increased quality of the solution. This in turn will motivate the maintainers to better understand the business concerns of the new contributor.
By contributing, the contributor will gain insights in the workings of the solution, thus increasing the quality of the product itself. (As an analogy: by taking apart an amplifier, you increase your understanding of the way the product satisfies your needs).
Last but not least, contributing generates good-will, subsequently increasing the probability of adequate answers to support questions.