Sounds more like an inconsistent enforcement of inconsistent rules. They probably have a guy they pay to clean up the ads and they are applying the rules as they see it. Anyhow, they technically can't prevent the sale of mining equipment because it does have other uses - not that SHA256 encryption cracking is a high demand market outside the NSA.
Well , they can prevent the sale of mining equipment on their website by doing something like above.
I don't consider video cards mining equipments any more , since we talk about bitcoin. And asics are asics , you can't do anything else with them.