If someone wants fixed, known deliverables, the last thing they should be looking at is proprietary software, where a seemingly stable product suddenly updates and everything is different and the license changes retroactively, e.g Photoshop. Version controlled, open source means you can check out any version you might need, at any time, now and forever. Seems worth throwing some money at such a promise.
Possibly a better phrasing would be "An open source ecosystem is worth investing in to hedge against the risk of license and source changes by the vendor"
If you are short sighted enough to only care about day to day operations and don't see competence in software usage as an investment that will bring competitive advantages in the long run.
Your competitive advantage is your staff, not your software. A company like Pixar only has so many proprietary tools because they've been around so damn long that rolling their own was the only way to go to get the results they wanted.
Even then, Pixar's advantage was the people they hired and allowed to thrive... not Renderman.
