You can produce work that looks good, as they technically have the features, but the workflow is generally atrocious for open source tools. This means it takes a lot longer to do stuff.

On top of this, the technical limitations of GIMP and Blender are much more limiting than what high-end apps like Nuke/Mari for texture painting (want to do 32k x 32k texture painting at full 32-bit float for RGBA), and things like XSI rending to PRMan or Arnold, kicking around 200GB of geometry at render time.

GIMP and Blender can't get anywhere near those use-cases - yes, they're extreme, but those are the things companies like ILM, SPI, Weta, Framestore, etc deal with on a daily basis.

This is good to know. I assumed Blender and GIMP had workflows with comparable efficiency once you got used to them. I've never used the commercial tools.

Gimp I don't care for, but the workflow in Blender is fairly good really.

I don't think it's the technology at all. It's improving all the time and being refined, and people are understanding how to use the technology better.

My theory is that instability in the industry caused by the studios is what's leading to very uneven work. Some of these studios will pay top dollar for big name actors and directors but are willing to have a bunch of random VFX companies from all over the world try to work together to build a coherent vision.