But that argument falls apart when you consider that Intel doesn't, and more importantly can't, use CUDA either.
CUDA's been slowing down lately and open-sourced alternatives are picking up, namely openCL. Unlike CUDA which can only be used on nVidia hardware (which makes it utterly useless for the mobile platform) the open-sourced software can be bridged to nearly all hardware regardless of who makes it.
Don't mistake CUDA's popularity in HPC with CUDA's overall popularity. CUDA was essentially the first to truly support GPGPU in a large fashion and the HPC community ate it up. You're right in that AMD doesn't push their chip's proprietary anything but that's why other companies along with AMD push forward the open-sourced stuff. Hell, the reason openCL was started and is succeeding is due to Apple and in a very un-Apple-like fashion, it's available to everyone.
CUDA's going to fall apart. There's no reason for another x86-like monopoly when you lock yourself out of any competition and charge inflated prices (Tesla). nVidia got hammered by GCN, make no mistake. nVidia locked themselves in a room with their shiny toy and asked everyone to pay a fee to get in but consumers have been realizing they can find much the same toys in other rooms that don't charge anything at all.
Even nVidia realized this wasn't the brightest move and that their strategy needed fixing.