I'm not sure if open sourcing the data is absolutely necessary to reproduce the results given access to the prediction API. "Stealing Machine Learning Models via Prediction APIs" (https://arxiv.org/abs/1609.02943) examines techniques in this space. The API might also be used in adversarial training. The underlying data would be useful for advancing research, but not necessarily a prerequisite for reproducing the API.

AWS wins not because they have created an impenetrable black box, but because the economics of reverse engineering (and maintaining) are not cost effective for the majority of users.