Yes, but they're benchmarking those 2x $4k CPUs (which you're complaining about) against a v100 GPU, which costs $7-11k — so where's the problem here? It's not like they're comparing their $8k/worth of CPU against a consumer GTX 1080.
Furthermore, there's nothing in their paper that seems to indicate that their new algorithm cannot be generalised to tasks other than recommendation. (Although admittedly I may have missed something)
