Why would it be hard to implement? They'd just have to count how many times specific boards are mentioned by specific table rows. edit: on their showPosts page.
Assuming they actually scrape the post histories of 500+ users every few hours. This being Yobit, I wouldn't be surprised if they do something cheap, like checking the post count on the profile. And they don't even verify simple things like neg trust so the chances of them being able to improve the scraper are slim.