The companies pay $300 or so for a special one with their logo; they still feel special so do not mind a version floating around with a generic logo on the crystal.
If anything, I have a feeling it's the exact opposite. It's more likley that the corporations would throw a fit if they knew that other people were able to get a crystal version (generic or not) for next to nothing when they're having to shell out $300 a pop for their customized version.