[Athas]

Modern AMD and NVIDIA GPUs are fairly similar hardware-wise, and it is not hard to write OpenCL code that executes efficiently on both. I agree that it is pretty hopeless to write performance-portable OpenCL across entirely different architectures, however.

[mattkrause]

Sure, but if you go with nVIDIA, you also get access to all the other goodies they distribute (thrust, cudaFFT, cudaDNN, etc) and all the CUDA-compatible stuff other people have written, like Theano and TensorFlow.

It does seem like people have gotten a little more interested in OpenCL lately, but it still lags pretty far behind. As dharma1 says below, AMD seems weirdly uninterested in catching up. If I were in change of AMD, I'd be throwing money and programmers at this: "Want to port your library to OpenCL? Here, have a GPU! We'll help."