Specialized ASICs are not easy to come up with, what's more if it's in a tug of war you can expect those to suddenly become obsolete, rendering this approach too costly for a scrapper. Also you may have missed the part in the original link where they were using AWS to do the scrapping, so no ASICs there, and you pay by the minute, two things that would make PoW a valid countermeasure, no "free computation" in that setup.